At least 21 people drowned after a boat capsized off the coastal town of Tanur in the Malappuram district of India’s southern state of Kerala, local authorities said on Monday.

The boat, which was carrying about 40 inbound passengers, overturned as it was overcrowded, said Abdul Nazar, Malappuram district’s junior superintendent of police.

It was not immediately clear exactly how many more people had died, the police office officer said, adding that about 10 passengers were currently being treated in various hospitals and many had been sent back after first aid.

The death toll was likely to rise as the boat was stuck in muddy waters and was being pulled out to rescue those trapped inside, Kerala’s minister for fisheries and harbour development, V. Abdurahiman told reporters.

The incident in the Malappuram district of the state took place at around 7pm local time on Sunday and a team from the National Disaster Response Force was at the site, a Kerala State Disaster Management Authority (KSDMA) spokesperson told Reuters.

“Pained by the loss of lives due to the boat mishap in Malappuram, Kerala,” Indian Prime Minister Narendra Modi said in a tweet.