Over 100 whales, swept ashore on Sri Lanka's beaches on Monday, were rescued by Tuesday morning and pushed back to sea after a nearly 18 hour rescue mission, but four whales died, the navy said here.

Sri Lankan Navy soldiers try to push back a stranded pilot whale into the deep water in Panadura on November 3, 2020. (Photo: AFP)

Navy Spokesperson Captain Indika De Silva told Xinhua that nearly 120 whales had been washed ashore on the Panadura beaches, just on the outskirts of capital Colombo, on Monday afternoon and the navy as well as the coast guard were immediately alerted by residents in the area.

This was Sri Lanka's largest mass stranding of whales, marine biologists said.

Nearly 70 navy and coast guard personnel along with civilian groups had been involved in the rescue mission and the last whale was pushed back to sea by 8 am local time on Tuesday.

"We worked throughout the night and by the morning we successfully pushed the last animal into the sea. A lot of civilian groups also assisted us. Unfortunately, we found four carcasses," De Silva said.

The carcasses had been found on the Panadura beaches and the beaches of Wellawatta and Wadduwa.

Marine biologists are conducting investigations on how the whales had been washed ashore.