The 17,000-ton Maersk Alabama, shown in an undated photo when it was operating under the name Maersk Alva, was hijacked by Somalia pirates as it sailed from Salalah, Oman, to Mombasa, Kenya. (Maersk Line/Associated Press)American crewmembers of a Danish cargo ship hijacked Wednesday morning by Somali pirates have retaken control of the vessel, but the captain is still being held hostage, said reports.

"Right now, they want to hold our captain for ransom, and we are trying to get him back," second mate Ken Quinn told CNN. "We had one of their hostages, we had a pirate. We took him for 12 hours. We tied him up. We returned him. But they didn't return the captain."

"Right now we are trying to offer them whatever we can, food. It's not working too good."

Capt. Richard Phillips is reportedly being held in a smaller boat.

A U.S. Navy warship has arrived off the coast of Somalia, said a spokesman for the owner of the Maersk Alabama cargo ship. The destroyer USS Bainbridge is on the scene, Kevin Speers said, adding the boat with the pirates is floating near the Maersk Alabama.

Dawn is only a few hours away in Somalia and officials are waiting to see what happens when the sun comes up, he said. Earlier Wednesday, U.S. officials said the 20-member crew had managed to successfully negotiate their own release.

"The crew is back in control of the ship," a U.S. official said at midday, speaking on condition of anonymity because she was not authorized to speak on the record.

Capt. Richard Phillips of Underhill, Vt., is the captain of the U.S.-flagged cargo ship Maersk Alabama, which was hijacked Wednesday by Somali pirates off the Horn of Africa. (Family handout/Associated Press)

At a noon news conference in Virginia, John Reinhart, the CEO of ship operator Maersk Line Ltd., said that the company was working to contact families of the crew. He refused to say whether the ship was back in the crew's hands.

"Speculation is a dangerous thing when you're in a fluid environment. I will not confirm that the crew has overtaken this ship," he said.

U.S. President Barack Obama was following the situation closely, foreign policy adviser Denis McDonough said.

The U.S. navy said the Danish-owned, U.S.-flagged ship was seized off the eastern coast of Somalia early Wednesday.

The 17,500-tonne vessel was en route to the Kenyan port of Mombasa, said the ship's operator.

The attack happened early in the morning, about 450 kilometres southeast of the town of Eyl in Somalia's Puntland region, the navy said.

No indication of response

Cmdr. Jane Campbell, a spokeswoman for the U.S. navy's Bahrain-based 5th Fleet, said that it was the first pirate attack "involving U.S. nationals and a U.S.-flagged vessel in recent memory." She did not give an exact time frame.

Andrew Mwangura of the East African Seafarers' Assistance Program said the ship was taken about 640 kilometres from the Somali capital, Mogadishu.

The ship is the sixth to be seized within a week, a rise that analysts attribute to a new strategy by Somali pirates operating far from the warships patrolling the Gulf of Aden, one of the world's busiest shipping lanes.

A dozen warships from countries including Britain, France, Germany, Iran and the United States dot the now notorious waters in the gulf in an attempt to deter pirate attacks.

Piracy has taken an increasing toll on international shipping, especially in the Gulf of Aden.

Pirates made an estimated $30 million US by hijacking ships for ransom last year, seizing more than 40 vessels off Somalia's 3,000-kilometre coastline.

With files from the Associated Press