Twenty people, including women and children, were killed when a houseboat with more than 30 passengers on board capsized and sank near the Thoovaltheeram beach in the Tanur area of this Kerala district on Sunday, the state government said.

Sports Minister V Abdurahiman said 20 deaths were confirmed on the basis of information from various hospitals where those pulled out from the water and inside the boat were admitted.

Four persons in critical condition have been admitted to a Kottakkal hospital here, Abdurahiman said.

Of the 20 bodies, 15 have been identified, the minister added.

"The boat is being hauled ashore and more bodies are expected to be recovered from inside," he told PTI.

Abdurahiman said many of those who died were women and children who had come for a ride amid the ongoing school vacations.

Prime Minister Narendra Modi has condoled the deaths and announced an ex-gratia of Rs 2 lakh to the next of kin of each victim.

"Pained by the loss of lives due to the boat mishap in Malappuram, Kerala. Condolences to the bereaved families. An ex-gratia of Rs 2 lakh from PMNRF (Prime Minister's National Relief Fund) would be provided to the next of kin of each deceased," Modi was quoted as saying in a tweet by the Prime Minister's Office.

Earlier, PK Kunhalikutty, an MLA of the Indian Union Muslim League (IUML), said the toll is expected to go up as rescue operations continue.

"It is a very tragic and unfortunate incident," the former minister said.

Speaking to reporters from a government hospital near Tanur here, he said overcrowding is believed to have been the reason behind the vessel capsizing.

Boats are not supposed to go out for rides after 6 pm but it is believed that the rule was violated in this case, he added.

Health Minister Veena George has called an emergency meeting following the accident to assess the situation, the state government said in a statement.

George instructed that expert treatment be ensured for the injured and the post-mortem process sped up so that the bodies can be released quickly to the next of kin, the statement said.

The post-mortems will be conducted at Tirur, Thirurangadi, Perinthalmanna hospitals and Mancheri Medical College by bringing sufficient staff, including doctors, from districts such as Thrissur and Kozhikode, it said.

The minister has issued strict instructions to conduct the post-mortems from 6 am and, if possible, at the private hospitals also where some of the bodies have been kept, according to the statement.

Speaking to reporters earlier, Abdurahiman had said, "More victims are believed to be trapped under the boat and have to be brought out. The boat had overturned. The reason for it is not yet known. The police will investigate it."

He is coordinating the rescue operations along with Tourism Minister PA Mohamed Riyas.

Chief minister Pinarayi Vijayan issued a statement condoling the deaths and directed the district collector to carry out a coordinated emergency rescue operation.

Fire and police units, officials from the Revenue and Health departments and local residents from Tanur and Tirur were involved in the rescue operation, the statement said.

The Chief Minister's Office said Vijayan will visit the site on Monday.

According to the statement, Monday has been declared a day of official mourning and all government programmes stand postponed as a mark of respect to the victims.

The incident occurred around 7 pm near an estuary close to the Thoovaltheeram beach in Tanur, the police said.

Those rescued were admitted to nearby private and government hospitals. The exact cause of the accident is not known at present, they added.