At least 15 people have died after a boat carrying dozens of people sank on Lake Kariba in Zimbabwe, with rescue operations continuing, officials have said.

Police said 90 passengers and five crew were onboard the vessel when it capsized on Tuesday, but it may have been overloaded, with other reports pointing to a higher number based on the registered ticket sales.

The vessel was hit by a strong wave and overturned, police added. Footage shared online appears to show the hull floating in the water.

Lake Kariba, which straddles the border with Zambia, is one of the world's largest man-made reservoirs, supporting transport and fishing and providing vital hydroelectric power to both countries.

The Zimbabwe Civil Protection Unit (CPU) said that registered ticket sales showed 114 adults were on the vessel. There could also have been an unknown number of children below ticketing age, it added.

The CPU said that 77 passengers had so far been rescued, and 15 bodies had been retrieved.

Two funeral parlours were collecting the bodies, it added.

Mutsa Murombedzi, a local member of parliament, posted a video on X of what she said was the boat at the start of the journey, adding that residents had been using it to travel across the lake to Kariba town, a journey that takes about five hours.

"We have very hard questions that require honest answers. The officials must release the correct number of people who were onboard," she wrote.

Police said more details would be released "in due course".