DAKAR, Senegal — Julius Ikena’s trade business is at a standstill because he cannot make electronic payments to his partners. Andrew Mofor cannot get access to the small fortune — 800 euros, or about $850 — that his daughter sent him through an online banking system.

And Angela Atabong, a 29-year-old economics student in Cameroon’s capital, can no longer tap out sweet nothings on the internet messaging service WhatsApp to her fiancé, who lives six hours away.

All three have been thwarted by Cameroon’s government, which is the latest in sub-Saharan Africa to switch off the internet in parts or all of a nation, or to put other limits on online communication in hopes of snuffing out protests and other opposition.

Officials in Cameroon and elsewhere say internet blackouts are a security measure. But they are also a hit to the fragile economies of developing nations that are increasingly reliant on online business transactions as internet access and cellphone use have exploded in recent years.

Authoritarian regimes have long limited communication with the outside world during tense times. Most notably in 2011, Egyptian government officials cut internet and mobile network access to 80 million people as thousands of protesters gathered in Tahrir Square in Cairo. Governments in Myanmar, Nepal and other countries have also shut off internet access in recent years.

Now, sub-Saharan African governments are increasingly employing the tactic: Blackouts have grown most rapidly in the past two years, researchers say.

In recent months, governments in several countries have turned off internet access during elections when violence broke out or was merely expected.

In December in Gambia, the president at the time, Yahya Jammeh, a ruthless leader known for human rights abuses, shut off internet services and blocked international cellphone calls as votes were cast in a presidential election that eventually ousted him from office. In Gabon, officials cited security concerns for an internet blackout during presidential elections that prompted deadly demonstrations after the vote was considered by observers to be fraudulent.

And in the Republic of Congo, internet access was blocked, television networks switched off and the nation’s main airport closed during an election that spurred violence. Government officials were accused of using airstrikes on opposition forces.

Elsewhere on the continent, Ethiopia has shut down some social media sites and internet services after demonstrations. In Zimbabwe, after protests over the travails of daily life, officials raised prices on cellphone data, a move widely seen as an effort to curb the use of social media. Lawmakers also pushed measures to allow the police to intercept data and seize electronics like laptops and cellphones, levying charges of terrorism for misuse. The Democratic Republic of Congo has blocked social media sites and text messaging amid demonstrations over the president’s attempts to extend his tenure in office.

Freedom House, an American watchdog organization, said in its annual Freedom on the Net survey of 65 countries that 24 nations experienced restrictions on social media and communications last year, up from 15 countries the previous year. Network shutdowns occurred in 15 countries last year, more than double that in 2015, the survey found.

Mai Truong, program manager for the survey, said, “It’s a strategy that the authorities are increasingly turning to as a method of controlling both the information landscape and citizens’ ability to mobilize, in recognition of the fact that the internet has become a fundamental tool for people to realize their rights and participate meaningfully in society.”

The United Nations Human Rights Council last year condemned the practice of intentionally preventing or disrupting access to information on the internet, saying access was a fundamental human right.

Network blackouts also have economic consequences. Many residents of some regions of Africa where joblessness is soaring are increasingly using online or mobile transfers to receive money from relatives in urban areas or abroad. If the internet is shut off, users cannot use Wi-Fi to transfer cash and must pay for mobile data to go online. The cost is prohibitive for many people.

Between July 1, 2015, and June 30, 2016, 81 short-term internet shutdowns in 19 countries cost at least $2.4 billion in gross domestic product globally, according to Darrell M. West, founding director of the Center for Technology Innovation at the Brookings Institution.

“As the digital economy expands, it will become even more expensive for nations to shut down the internet,” he wrote in an October analysis. “Without coordinated action by the international community, this damage is likely to accelerate in the future and further weaken global economic development.”

Mr. West estimated that the election-time shutdown last year in the Republic of Congo alone dealt an $72 million hit to the economy of the struggling nation.

Cameroon’s continuing internet blackout affects only English-speaking regions of the country. It followed weeks of protests from lawyers, teachers and other residents in those areas who have been agitating for better treatment from the French-speaking government, which they say has long marginalized their communities.

Before independence in the early 1960s, Cameroon was colonized by the French and the British. The Constitution allows protections for both languages, but Francophones rule the government. Most official documents are offered in French and not translated, evidence that Anglophones cite as proof of their marginalization.

Some demonstrations in English-speaking areas have turned violent, and security forces have fired on protesters.

The blackout has attracted attention from Edward J. Snowden, the former intelligence contractor who revealed extensive surveillance and data collection programs operated by the National Security Agency. He recently criticized Cameroon’s government on Twitter, saying, “This is the future of repression.” A hashtag #BringBackOurInternet has been circulating.

Yet the shutdown is a stopgap measure until another filtering system can get up and running, said one diplomat with knowledge of operations in the region, who declined to be identified because of continuing tensions there. The government is buying technology from Chinese companies that will allow officials to filter websites in the same fashion that the Chinese government has long employed to control content.

Still, the blackout could have political ramifications for Cameroon’s government. Bankers have largely stayed apolitical over the more than three decades since President Paul Biya has been in office. But as the shutdown starts to hurt their business, they could become a potent adversary, analysts fear.

The blockage has also made it difficult for local journalists to report on what is widely viewed as an overly harsh government response to the demonstrations.

Before the internet went dark, some cellphone users received ominous messages from officials.

“Dear subscriber,” one message the government circulated on WhatsApp warned. “You incur six months to two years imprisonment and 5 to 10 million fine if you publish or spread on the social media information that you can’t prove.”

Another message read, “Do not be an accomplice of disinformation or destabilization of our country through the social media.”

Some citizens in blackout areas have come up with clever ways to get around the shutdown. Cellphone users type out messages and then pay drivers who gather garbage bags full of phones and take them outside the blackout boundaries. After crossing into an area where the network is up and running, they hit the send button on each phone.

Since the blackout, Henry Boh has not been able to send money to Bamenda in the northwest, where his brother needs cash to take his nephew to the hospital for treatment.

“This is a clear sign that the government of Yaoundé doesn’t listen to its people’s voices,” said Mr. Boh, who lives in Yaoundé, the nation’s capital.

Mr. Boh said the shutdown further proved the Anglophone protesters’ point that the government mistreated them. In the nation’s Far North region where Islamic militants from Boko Haram wage deadly attacks, they say, the internet is operational.

“The government respects Boko Haram more than us,” Mr. Boh said.

Dionne Searcey reported from Dakar, Senegal, and Francois Essomba from Bamenda, Cameroon.