A cruise boat which sank in Lake Victoria was overloaded, carrying about 120 people instead of its capacity of just 50, Uganda's president said on Sunday.

At least 29 people were confirmed dead after the accident, while 26 others had been rescued, President Yoweri Museveni said on his Twitter feed, adding that the operators of the boat would be charged with criminal negligence and manslaughter. 

Police had said on Saturday at least 10 people were dead following the accident off Uganda's Mukono district, close to the capital Kampala.

"The boat was overloaded and secondly there was bad weather," Patrick Onyango told Reuters, adding the boat was carrying 84 people.

Another 26 people had been rescued from the water, Onyango said, a lower figure than the initial 40 given by the police on Saturday. He attributed the discrepancy to some survivors' failure to register with the police.

"Our rescue team is still on the ground trying to rescue whoever we can find," he said.

Among those rescued on Saturday was Prince Daudi Kintu Wasajja, a brother of Ronald Mutebi, the king of Buganda kingdom, Uganda's largest, police said.

The East African nation has several kingdoms, whose kings wield considerable social clout but little political influence.