A boat carrying a school group capsized in a lake in western India on Thursday, drowning 15 pupils and one teacher, fire service officials said.

Eleven students were rescued when the boat capsized in Harni Lake in the city of Vadodara, and rescuers were searching for person who was still missing, fire officer Jitu Parmar said.

The cause of the accident is being investigated.

“The incident of children drowning after the boat capsized in Vadodara’s Harani Lake is extremely heart-breaking,” said the state’s top elected official, Bhupendrabhai Patel.

Vadodara is a a city known for the diamond trade in Gujarat state.

Indian media reports said the students there were on a picnic when the accident occurred.

Boating accidents are common in India, where many vessels are overcrowded and have inadequate safety equipment.

Last September, 22 people drowned when a double-decker boat carrying more than 30 passengers capsized near a beach at a coastal town of Kerala state in southern India.

In May 2018, 30 people died when their boat capsized on the swollen Godavari River in the southern state of Andhra Pradesh.