The US Coast Guard pressed a search Tuesday for survivors of the El Faro cargo ship sinking, but warned that "every passing hour" reduced the likelihood of finding alive any of its 33 crew members.

On Monday, Coast Guard officials said the ship was believed to have sunk in the Atlantic and that human remains had been identified in one survival suit found in the ocean.

"This is still an active Coast Guard search and rescue case," Coast Guard Chief Petty Officer Jon-Paul Rios told AFP.

"With every passing hour it does become more difficult to bring home survivors but at this time the important thing is that we are still searching," he added.

The 735-foot El Faro, which was carrying 28 Americans and five Poles, lost contact early Thursday en route from Florida to Puerto Rico as Hurricane Joaquin approached the Bahamas.

It was reported to be caught in the storm near the chain's Crooked Island, where the ship sent a satellite notification stating it had lost propulsion and had a 15-degree list.

The Coast Guard Monday said a number of items had been found scattered at sea, among them a recovered life ring and life boat from El Faro.

It added that searchers had also been able to check life rafts, life boats and survival suits, looking for signs of life.

Survivors can usually stay alive in warm water conditions for four to five days, a Coast Guard official said.

However, Tuesday marks five days since the ship was last heard from.

The Coast Guard said four aircraft, a helicopter and three cutters were searching for survivors, in addition to three tugboats sent by the shipping company that owns El Faro.

"At this time we've searched more than 160,000 square nautical miles, that's larger than the state of California" Rios said.

The US National Transportation Safety Board on Tuesday sent a team to Jacksonville, Florida to begin an investigation.

"There is a huge debris field, so the investigators hope to find as much as possible," NTSB Vice Chairman Bella Dinh-Zarr told local television channel WJXT.

"It's a big challenge when there is such a large area of water and at such depths."

Joaquin, the Atlantic hurricane season's most powerful storm so far, caused serious damage in the Bahamas and power outages in Bermuda.

The hurricane, now weakened to a Category One storm on the five-point Saffir-Simpson scale, is swirling in open waters in the North Atlantic. Forecasters expect it to be downgraded Wednesday to a tropical storm.