MANILA (AFP)

The Philippines said it had grounded the passenger fleet of a local shipping line on Tuesday pending an investigation, as rescuers scoured the ocean for survivors of a ferry sinking that killed at least 18 people.

The MV Trisha Kerstin 3 was carrying 344 passengers and crew when it went down off southwestern Mindanao in the early hours of Monday. Most people were rescued in the immediate aftermath.

The 10 passengers still unaccounted for include the ferry's captain, eight crew members and a safety marshall, Philippine Coast Guard Commandant Ronnie Gavan said at a press briefing on Tuesday.

The triple-decker vessel sank on nearly the same route where 31 people died in 2023 after a fire aboard the Lady Mary Joy 3 ferry. Both ships were owned by locally based Aleson Shipping Lines.

Transportation secretary Giovanni Lopez said on Tuesday that the company's passenger fleet would be kept at port pending an investigation.

"As of now, the entire passenger fleet of Aleson Shipping Company (is) grounded," he said, adding that the country's maritime regulator and coast guard would conduct a safety audit over the next 10 days.

"The president has ordered a full-blown investigation, so all the angles will be looked at to determine what really happened," he said.

"If it turns out the shipowners were deficient, they will expect the full force of the law," Lopez told reporters.

He added that there had been 32 recorded safety "incidents" at sea involving the company but offered no specifics.

The coast guard's Gavan said that ongoing search-and-rescue efforts remained the immediate priority.

"The most important thing at this point is lives," he said, adding that 16 technical divers and a remotely operated vehicle were being flown in from Manila to assist in the coming investigation.

A coast guard press aide told AFP that the ship was believed to be sitting at a depth of about 76 metres (249 feet).

An Aleson Shipping Lines employee who answered the phone said the company would release a statement addressing the situation within the day.

'Negligent'

On Monday, a survivor of the sinking told AFP that "no one from the crew alerted us", describing the panic that gripped passengers as the ship began tilting in the water.

Aquino Sajili said passengers had raced to one side of the ship in a desperate attempt to rebalance it before he heard a "loud snap" that preceded the ship's rapid sinking.

Those who survived then spent hours bobbing in life jackets or clinging to other floatation devices while awaiting rescue, the 53-year-old lawyer said.

The Philippines has a long history of disasters involving the inter-island ferries that ply its seas.