A total of 42 people have been confirmed dead after a ferry sank in Tanzania's Lake Victoria, a government official has announced, adding that more than 200 people are actually believed to have drowned.

Emergency teams were dispatched to the scene but have halted rescue operations until dawn on Friday, Ukerewe District Commissioner Colonel Lucas Magembe told Reuters.

A local official cited by the BBC said the vessel was overloaded with more than 400 people, with other reports stating that some 300 passengers were on board.

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The exact number of people on board is difficult to determine, with Reuters reporting that the person dispensing tickets was among those who drowned, and that recording data has also been lost.

The MV Nyerere ferry overturned near the shore between the islands of Ukora and Bugolora.

"We pray to God to give us hope in such an accident," Regional Commissioner Adam Malima told reporters."We pray to God to give us hope that there has not been a high death toll."

Theresia Mwami, a spokesperson for the national ferry services operator TEMESA, said that maintenance had been carried out on the ferry in recent months, with two engines overhauled.

The country has been faced with similar tragedies in the past, with at least 145 people dying in a ferry disaster in the semi-autonomous archipelago of Zanzibar in the Indian Ocean in 2012. That boat was also overcrowded.

In 1996, a ferry tragedy in the same area of Lake Victoria killed at least 500 people.

Lake Victoria is Africa's largest lake by area, and the world's second largest fresh water lake by surface area, after Lake Superior in North America. It is a popular attraction for tourists, with many local companies offering boat trips to spot wildlife, ranging from hippos to exotic birds.