MANILA, Philippines (CNN) -- Filipino authorities hope that 749 people missing after their ferry capsized in a typhoon are still alive inside an air pocket, the head of the country's Red Cross said Sunday.
"It's a race against time," said Sen. Richard Gordon, who is head of the Philippines Red Cross.
"There is a bubble in the ship's bowels that are now on top of the surface of the water, and we are now trying to get assistance from our own government to get divers down into the vessel as soon as the seas calm," he said.
Typhoon Fengshen has killed between 120 and 150 people in the Philippines, he said, noting that he has not heard from Red Cross chapters in the country's remote areas.
The Filipino government may ask the U.S. Navy to send in seaborne helicopters and divers who can help "recover people who may be alive under the ship," Gordon said.
The crew of the MV Princess of Stars reported Saturday that it ran aground after its engine failed during its regular run between Manila and Cebu City, according to Vice Adm. Wilfredo Tamayo.
Radio contact with the ship was lost Saturday afternoon, Coast Guard Lt. Cmdr. Armando Balilo said.
The ferry capsized near the central Philippine island of Sibuyan, carrying 130 crew members and more than 600 passengers, Gordon said. Only four survivors and 10 bodies have been found, he said.
The effort to reach the ferry has been slowed by rough seas stirred up by Typhoon Fengshen, which made landfall in the eastern Philippines early Saturday.
The ferry, which can weather rough seas, embarked during "Typhoon signal No. 1," which indicated there was no impending danger, Gordon said.
"But unfortunately the typhoon suddenly turned and it [became] Typhoon signal No. 3, which has now created a really, really bad problem," he said. "After that, I think the ship ran into some problems -- we're not sure about that yet -- and it drifted to seashore, ran aground and eventually capsized."
The families of the ferry passengers are "very bitter about the situation," he said.
"Obviously there's a lot of angry people among the ship's families, and I just spoke with them," he said, adding that he told grieving relatives that the Red Cross is there to "alleviate human suffering and we're doing our best right now to try to get that done."
"But we still have to reckon with the fact that the typhoon is still ravaging central Luzon."
Typhoon Fengshen was reported to have top sustained winds of 110 mph, though the storm lost strength after moving ashore.
Fengshen is still moving across the Philippines, dumping torrential rains fueled by 75 mph winds as it pushes toward Manila, according to the Filipino Atmospheric Geophysical and Astronomical Services Administration.
