Rescue efforts are under way in the Philippines after a inter-island ferry carrying 251 people sank off an island south of Manila.

Four people died when the craft went down, according to local media reports.

The rescue was launched on Thursday after the passenger vessel Mercraft 3 reportedly began sinking between Quezon province's Infanta town and the ferry's destination, Polillo island, coast guard spokesman Armand Balilo said.

He said coast guard was coordinating with the military for the possible deployment of air force helicopters and naval ships to the scene.

A survivor, Donel Jade Mendiola, told DZMM radio that the weather was fine when the ferry left port in Quezon's Real town, but strong winds and large waves started to batter it about two hours into the trip.

"The vessel came to a halt and started taking in water in the front side. The passengers dashed to one side and the ferry started to sink," Mendiola said.

The passengers were instructed to don life vests, he said.

Local fishermen have reportedly joined in the rescue efforts, which have been hampered by bad weather.

Boat accidents are common in the Philippines, with the archipelago regularly lashed by storms.