A man who survived a ferry disaster that claimed at least 46 lives on Zimbabwe's Lake Kariba told AFP on Thursday how he watched helplessly as people tried to save themselves, with his best friend and seven of his relatives among the dead.

The overloaded ferry – a vital link for villagers and fish traders around the vast lake – overturned on Tuesday in one of the country's worst passenger boat disasters.

"A wave pushed the sinking vessel and we managed to climb on top," Chance Siyamavhu said at a memorial service in the lakeside town of Kariba, close to the border with Zambia.

Perched on the upended boat, he watched as passengers struggled to survive, unable to save them.

'Not in a position to help'

"When the boat capsized, most of the people scrambled to get the life jackets but most of them did not even know how to use them," the 45-year-old told AFP. "Most people could not make it."

"Our relatives were swept in another direction and they sank because we were not in a position to help them," he said.

Another survivor, Norah Chadenga, 56, a fish trader who travelled from Harare with her sister-in-law to buy fish for resale, was overcome with grief as she mourned the woman.

Chadenga said she had encouraged her sister-in-law to join the business so she could raise money for her son's university education.

'In pain'

"I am in pain. I regret asking her to try the fish business. She died before she could raise a single cent. Maybe if she had pursued another business idea, she would still be alive today," she said.

Lake Kariba straddles the border between Zimbabwe and Zambia, more than 300 kilometres northeast of the capital Harare, and is the world's largest man-made lake by volume.

The vessel transported people between the northern town of Kariba and islands and fishing villages around the vast stretch of water, with locals telling AFP that accidents are rare.

Such ferries are a vital link for villagers and traders travelling between remote rural communities and Kariba's commercial hub.

President orders ferry's replacement

Local Government Minister Daniel Garwe, who officiated the memorial, said President Emmerson Mnangagwa had directed the government to replace the ferry and urgently repair the road linking Kariba and Chalala.

"The boat belongs to the government," and Mnangagwa had "directed that a replacement passenger ferry be found and that an impassable road linking Kariba, Siakobvu and Chalala be urgently fixed", he said.

Dozens of mourners gathered in front of 44 coffins at the emotional service, as police announced that the death toll had risen to 46.

"The names of the victims who perished in the accident will be released in due course," a police statement said.

Overcrowded vessel

Officials say the boat was authorised to carry 90 people but was packed with 114 adults, five crew members and an unspecified number of children.

The civil protection unit said 77 people were rescued, and there were fears that other passengers may be unaccounted for.

Survivors said they had pleaded for the captain to turn back as the ferry took on water.

Anymore Chambati, who had been a security official on the vessel, told AFP he had tried to hand out life jackets as the ferry began to sink. "I managed to only give not more than 10," he said. "The ferry engines were filled with water because of the heavy winds and eventually they failed, save for one."