At least 22 people have died after a packed tourist boat capsized in India's southern Kerala state.

The death toll could rise as rescue efforts are under way on Monday and the vessel is pulled from muddy waters.

Overcrowding caused the double-decker boat to capsize, Abdul Nazar, junior superintendent of police of Malappuram district, told Reuters.

The boat was reportedly carrying about 50 people, or double its capacity, when it overturned on Sunday night.

The police on Monday registered a case of culpable homicide against the owner of the boat, who is reportedly absconding.

Indian Prime Minister Narendra Modi expressed condolences on Twitter, saying he was "pained by the loss of lives".

Many passengers were trapped under the boat and the darkness held back rescue efforts, according to local media. The casualties included women and children on school holiday.

At least four people who were taken to hospital are in critical condition, said Kerala's sports and fisheries minister, V Abdurahiman.

The exact number of missing passengers was not immediately clear. Authorities said they were investigating the cause of the accident and are looking into whether the boat had a proper permit.

Shameer, a lifeguard involved in the rescue operation, told Mathrubhumi news channel that "the boat was completely upside down" when rescuers arrived at the scene. "I recovered four bodies and none of them had life jackets on."

Many of the other passengers were also not wearing life jackets at the time of the incident, survivors told local media.

Ambika, a resident of the nearby Tanur area, told Manorama news channel that when she first saw the boat approach, everyone seemed to be "cheering happily".

"But suddenly the lights went out, the boat sank and the cheers were replaced with screams for help," she said.

Ms Ambika added that she immediately called the police for help. "But we could not do anything beyond that because it was getting dark and there was no way to reach the passengers."

Boat accidents are not infrequent in India where vessels are often overcrowded, poorly maintained and lack safety equipment.

(editor-in-charge：Press center2)