Rescuers searched on Monday for survivors from an overcrowded tourist boat that capsized on a south Indian waterway with the death of at least 22 people, authorities said.

Police said the exact number of people on board the boat that capsized on Sunday evening in an estuary near the town of Tanur, in Kerala state, had yet to be confirmed. Police said they were searching for the owner of the boat who had absconded.

A man identified as Shafeeq, who was on board the converted fishing boat, told the Manorama News channel the vessel had listed badly soon after it set off.

"Most of the people on the upper deck jumped into the river and swam to safety," the man said.

According to initial estimates there were about 40 people, most believed to be domestic tourists, on board including several children, said Tanur police official Jeevan George.

"We're not clear about the total number of people on board the boat as the passengers included several children who did not need tickets," George said.

Famous for its picturesque backwaters, Kerala is a major destination for domestic and international tourists.

The state government and police said they had launched investigations into the accident.

Residents of the area said the cruise service had only been launched last month and it lacked safety measures. One man said he and his brother had decided not to go on the cruise because the boat looked too crowded.

"The operators were asking more people to join saying it was the last trip of the day," the man, identified as Ibrahim, told Manorama News.