At least 20 people have died after a powerful cyclone struck Madagascar, says the disaster authority in the Indian Ocean island.

Cyclone Gezani made landfall on Tuesday, hitting the island's main port, Toamasina.

Madagascar's disaster management office said there was "total chaos" - reporting that houses collapsed in the impact zone, where the bodies were found. Neighbourhoods were plunged into darkness as power lines snapped, while trees were uprooted and roofs ripped off.

The cyclone's landfall is likely to have been one of the most intense recorded around the city in the satellite era, according to the CMRS cyclone forecaster on France's Reunion island, cited by AFP.

The National Office for Risk and Disaster Management said many were killed when houses collapsed. Cyclone Gezani hit Toamasina - the country's second-largest city - with winds reaching 250 km/hour (155 mph).

"It's total chaos, 90% of house roofs have been blown off, entirely or in part," the head of disaster management at the Action Against Hunger aid agency, Rija Randrianarisoa, told AFP.

Madagascar's disaster management office has evacuated dozens of injured people and hundreds of residents from a district around Toamasina, home to 400,000 people.

Residents in and around Toamasina described scenes of chaos as the cyclone made landfall. "I have never experienced winds this violent... The doors and windows are made of metal, but they are being violently shaken," Harimanga Ranaivo told the Reuters news agency.

Gezani is the second cyclone to hit Madagascar this year. It comes 10 days after tropical cyclone Fytia killed 14 and displaced over 31,000 people, according to the UN's humanitarian office.

Ahead of the cyclone's arrival, officials shuttered schools and rushed to prepare emergency shelters.

Madagascar's meteorological service said on Wednesday morning that Gezani had weakened to a moderate tropical storm and had moved westward inland, about 100km (60 miles) north of the capital, Antananarivo.

"Gezani will cross the central highlands from east to west today, before moving out to sea into the Mozambique Channel this evening or tonight," the service said.

The country's new leader Colonel Michael Randrianirina, who seized power in October, was in Toamasina on Wednesday morning to assess the situation.

Cyclone season in the Indian Ocean around Madagascar normally lasts from November to April and sees around a dozen storms each year, AFP reports.