MANILA -- At least 15 bodies were recovered, and 43 people remained missing after an inter-island ferry carrying at least 350 people sank early Monday morning in waters off Basilan province in the southern Philippines, authorities said.

Philippine Coast Guard (PCG) Commander Romel Dua of the Southern Mindanao District told reporters that 316 people were rescued.

The PCG said the M/V Trisha Kerstin 3 was en route to Jolo Island in Sulu province from Zamboanga City when it sank before 2 a.m. local time on Monday off Balukbaluk Island in Hadji Muhtamad, a municipality in the Sulu Sea.

"The search and rescue operation is ongoing, but what I can say is that the ship is not overloaded. It has a maximum passenger capacity of 350, and the actual passengers on board, as declared by the master, are 332," PCG Chief Admiral Ronnie Gil Gavan told reporters in Manila.

He added that the PCG has immediately acted on the incident, saying that all rescue assets in the region are involved.

"There are casualties, but the details are not yet final," he said.

Gavan said the cause of the sinking was still under investigation.