Passengers on the aging, crowded boat headed for one of Tanzania’s top tourist destinations said they realized something was wrong when the overnight ferry began to list from side to side.

Then water rushed through and killed the engines, sending the M.V. Spice Islander upside down and pitching hundreds of people into the deep sea early Saturday. A witness counted nearly 200 bodies, and the president of the nearby island of Zanzibar said more than 570 people were rescued, suggesting that the boat was overloaded. Some survivors said the boat’s capacity was 600.

Those lucky enough to find something to cling to floated in the dark waters for at least three hours until the strong currents began to wash them up on the white sandy shores of Zanzibar. As the sun rose, news of the tragedy had already spread throughout the community and thousands of people were on the beach, desperately hoping their family members would be the next to emerge from the waves. One man — too upset to give his name — screamed over and over the names of 25 missing family members, including his sisters, wife and grandsons.

Throughout the day, police waded through the clear waters to shore, carrying bodies on stretchers, wrapped in brightly colored cloth and blankets. The smallest bundles — the children — they carried in their arms. Tourists on the popular island helped survivors, and local charities provided blankets and tea.

It’s unclear how many people were killed or how many people were on the boat when it capsized.

A reporter for ITV, a local television station, said he had seen 189 bodies. The president of Zanzibar, Ali Mohammed Shein, said 572 people had been rescued. He declared three days of mourning for the disaster. A survivor, Khamis Mohamed, said the ferry was carrying hundreds more than its official capacity of 600.

Others reflected that sentiment, some very vocally.

Dozens of Tanzanians on the island of Zanzibar expressed anger that the boat had been allowed to leave port and asserted that it was overloaded. Residents of Stone Town said they had frequently referred to the vessel as “a disaster waiting to happen.” Survivor Abdullah Saied said some passengers had refused to board the boat, saying it was too full, as it left the mainland port of Dar es Salaam for Pemba Island, north of Zanzibar.

— Associated Press