President Samia Suluhu Hassan has been declared the winner of Tanzania's presidential election, securing another term amid days of unrest across the country.

Samia won 98% of the votes in Wednesday's poll, the electoral commission said. In her Saturday victory speech she said the election was "free and democratic", accusing protesters of being "unpatriotic".

Opposition parties rejected the results, calling the vote a mockery of the democratic process as Samia's main challengers had been either imprisoned or barred from running.

International observers have expressed concern over the lack of transparency and widespread turmoil that has reportedly left hundreds of people dead and injured.

The nationwide internet shutdown is making it difficult to verify the death toll.

The government has sought to play down the scale of the violence - and authorities have extended a curfew in a bid to quell the unrest.

Receiving her victory certificate on Saturday, Samia, 65, said: "We thank the security forces for ensuring that the violence did not stop voting.

"The government strongly condemns the violent incidents. These incidents were not patriotic at all," she said.

Earlier on Saturday, electoral commission chief Jacobs Mwambegele declared Samia "the winner of the presidential election".

Samia secured about 31.9 million votes, or 97.66% of the total, with turnout nearing 87% of the country's 37.6 million registered voters, the electoral chief said.

In Tanzania's semi-autonomous archipelago of Zanzibar - which elects its own government and leader - CCM's Hussein Mwinyi, who is the incumbent president, won with nearly 80% of the vote.

The opposition in Zanzibar said there had been "massive fraud", the AP news agency reported.

Mwinyi's swearing-in ceremony is under way at Amaan Complex stadium in Zanzibar.

No protests were reported on Saturday morning, but tension remained high in Dar es Salaam, where security forces manned roadblocks across the port city.

On Friday demonstrators Dar es Salaam and other cities took to the streets, tearing down Samia's posters and attacking police and polling stations despite warnings from the army chief to end the unrest.

The demonstrations are mostly led by young protesters, who have denounced the election as unfair.

They accuse the government of undermining democracy by suppressing the main opposition leaders - one is in jail and another was excluded on technical grounds.

A spokesperson from the opposition Chadema party on Friday told AFP news agency that "around 700" people had been killed in clashes with security forces, while a diplomatic source in Tanzania told the BBC there was credible evidence that at least 500 people had died.

Foreign Minister Mahmoud Kombo Thabit has described the violence as a "few isolated pockets of incidents here and there" and said "security forces acted very swiftly and decisively to address the situation".

In a statement, the UN chief Antonio Guterres said he was "deeply concerned" about the situation in Tanzania, "including reports of deaths and injuries during the demonstrations". He urged all parties involved to "prevent further escalation".

The UK, Canada and Norway have expressed similar concerns, citing "credible reports of a large number of fatalities and significant injuries, as a result of the security response to protests".

There were two main opposition contenders - Tundu Lissu, who is being held on treason charges, which he denies, and Luhaga Mpina of the ACT-Wazalendo party - but he was excluded on legal technicalities.

Sixteen fringe parties, none of whom have historically had significant public support, were allowed to run.

Samia's ruling party Chama Cha Mapinduzi (CCM), and its predecessor Tanu, have dominated the country's politics and have never lost an election since independence.

Ahead of the election, rights groups condemned government repression, with Amnesty International citing a "wave of terror" involving enforced disappearances, torture, and extrajudicial killings of opposition figures.

The government rejected the claims, and officials said the election would be free and fair.

Samia came into office in 2021 as Tanzania's first female president following the death of President John Magufuli.