The two countries are separated by the narrow Palk Strait known for its jumbo prawns, with Sri Lankan fishermen long accusing their Indian neighbours of poaching in their territory.

The incident took place late Monday, with rescuers still searching Tuesday for one of the trawler's missing crew members, the navy said in a statement.

Two other fishermen from the boat were rescued, it said.

"The search and rescue operation is being augmented by a team of navy divers, fast attack craft and inshore patrol craft," the navy added.

On Sunday Sri Lankan fishermen took to the sea in a protest that called on authorities to block Indian fishing boats from their waters and end bottom trawling.

The practice -- banned from Sri Lankan waters in 2017 -- involves dragging heavy nets across the sea floor to catch a large volume of fish, damaging the marine ecosystem.

Sri Lankan fishermen were not allowed to venture out during much of the island's decades-long Tamil separatist war that ended in 2009, allowing Indians a free run in the area.

But there have been increasing tensions over poaching since Sri Lankan fishermen have been permitted at sea again.

The South Asian country has regularly detained large numbers of Indian fishermen and seized their boats, but there has been no let-up in poaching, according to locals.

Sri Lankan fishermen say every week, several Indian vessels enter their waters to fish.

An Indian fisherman was allegedly killed by Sri Lankan forces in March 2017.