Emergency services have been placed on alert and officials in Bermuda are reporting scattered power outages as Hurricane Joaquin lashes the island with winds and pelting rain.

As the storm faded in the Bahamas, the U.S. Coast Guard says rescuers have found what's believed to be debris from a cargo ship carrying 33 people that lost contact during the storm.

Rescuers spotted "life-jackets, life-rings, containers and an oil sheen" in the water early Sunday afternoon, the Coast Guard confirmed, as it expanded its search off the southeastern Bahamas for the El Faro. The vessel has not been heard from since it lost power Thursday and was taking on water in fierce seas churned up by the hurricane.

The owner of the missing cargo ship said Sunday afternoon that the container plucked from the water appears to be from the missing ship.

But Tim Nolan, president of TOTE Maritime Puerto Rico, said in a statement that "there has been no sighting of the El Faro or any lifeboats."

The Coast Guard has not yet confirmed that connection.

As darkness fell Sunday, two Coast Guard cutters planned to continue searching through the night after the planes and helicopters helping the rescue effort returned to their bases.

The El Faro left Jacksonville, Florida for Puerto Rico on Tuesday with 33 people aboard — five Polish and 28 Americans — when Joaquin was still a tropical storm.

In the last call from the ship on Thursday, the captain reported its propulsion was not operating and that a hatch cover had popped open, allowing water to enter the number three hold.

On Saturday night, the Coast Guard reported that a plane involved in the search located a life-ring from the El Faro about 120 kilometres northeast of the ship's last known position near the Bahamas. A Coast Guard helicopter recovered the object and confirmed it belonged to the missing ship.

Two other life rings were later retrieved from the same area, but it's not known whether they, too, were from the ship.

After rescuers found signs of the ship, family members of the crew gathered at a union hall in Jacksonville, Florida, to rally one another's spirits as news of the discovery circulated.

Laurie Bobillot, whose daughter, Danielle Randolph, is a second mate on the El Faro, said Sunday that she was trying not to lose hope after nearly four days spent anxiously waiting.

"We've got to stay positive," Bobillot said. "These kids are trained. Every week they have abandon ship drills."

Conditions in the area on Saturday hampered search efforts, with rough seas and winds in excess of 185
km/h, the Coast Guard said.

"This was the most challenging weather conditions anyone on our crew had ever flown," said Coast Guard pilot Lt Dustin Burton after returning Saturday from his mission.

In video released by the Coast Guard one pilot said visibility was less than half a kilometre while flying low at 300 metres.