More than 90 people died when an overcrowded makeshift ferry sank off the north coast of Mozambique, local authorities said on Sunday.

The converted fishing boat, carrying about 130 people, ran into trouble as it tried to reach an island off Nampula province, officials said.

"Because the boat was overcrowded and unsuited to carry passengers it ended up sinking. There are 91 people who lost their lives," said Nampula's secretary of state Jaime Neto.

Many children were among the victims, he added.

Rescuers had found five survivors and were searching for more, but sea conditions were making the operation difficult.

Most passengers were trying to escape the mainland because of a panic caused by disinformation about cholera, Neto said.

The southern African country, one of the world's poorest, has recorded almost 15,000 cases of the waterborne disease and 32 deaths since October, according to government data.

Nampula is the worst affected region, accounting for a third of all cases.

In recent months, the province has also received a large influx of people fleeing a wave of jihadist attacks in its northern neighbour of Cabo Delgado.

Neto said an investigative team was working to find out the causes of the boat disaster.

Two of the five survivors were receiving treatment in hospital, the official said.

The boat was headed to the Island of Mozambique, a small coral islet that used to serve as the capital of Portuguese East Africa and gave its name to the country.

A trading-post on the route to India initially used by Arab merchants, it was claimed for Portugal by famed explorer Vasco da Gama.

Hosting a fortified city and linked to the mainland by a bridge built in the 1960s, the island is listed as a World Heritage Site by the UN's culture agency, UNESCO.

Mozambique, which has a long Indian Ocean coastline and borders South Africa, Eswatini, Zimbabwe, Zambia, Malawi and Tanzania, was a Portuguese colony until independence in 1975.

Home to more than 30 million people, it is regularly hit by destructive cyclones.

In March, at least one person died as an illegal fishing vessel wrecked near a southern beach.

With almost two thirds of the population living in poverty, the country has set high hopes on vast natural gas deposits discovered in Cabo Delgado in 2010.

But an insurgency since 2017 waged by militants linked to the Islamic State group has stalled progress. More than 5,000 people have been killed and almost a million forced to flee their homes since fighting began.