American officials speaking on condition of anonymity, reported that the crew had retaken the vessel, though Maersk Line, the company that owns the ship, said it could not confirm the vessel was back under control of the crew.
"Speculation is a dangerous thing when you're in a fluid environment. I will not confirm that the crew has overtaken this ship," said Maersk Line Ltd. CEO John Reinhart.
Maersk Line did say it received a call around 11 a.m. EDT from the crew confirming that they were safe, according to Reuters.
The second in command on the ship called his father Capt. Joseph Murphy to tell him they had regained control, the Associated Press reported.
According to an anonymous U.S. official, one pirate was under crew control, three tried to flee and that others were reported to be in the water.
The attack is believed to be the first hostage-taking of American sailors in 200 years, according to the AP.
Cmdr. Jane Campbell, a spokeswoman for the U.S. Navy's 5th Fleet based in Bahrain, said the incident is the first to involve Americans "in recent memory."
A Pentagon spokesman would not discuss military plans and said there had been no communication with the pirates over ransom.
The attack is at least the sixth in a week by pirates off the Horn of Africa where it is hard for naval warships to patrol and defend ships from pirates, despite an increased presence of international navies.
The closest U.S. ship at the time was 345 miles away, according to Navy spokesman Lt. Nathan Christensen.
The Maersk Alabama was en route to Mombasa, according to a statement by A.P. Moller-Maersk, the world's largest container shipping company. The U.S. Navy confirmed to the AP that it was hijacked about 280 miles southeast of the Somalia town of Eyl - a hot spot for pirates.
The ship is owned and operated by Maersk Line Limited, a Virginia-based subsidiary of A.P. Moller-Maersk. The ship's route is between Oman, Djibouti and Mombasa, Kenya on the company's East Africa service.
The vessel was carrying 232 containers of relief food from the U.N.'s World Food Programme meant for Somalia and Uganda, a WFP spokesman told Reuters.
White House press secretary Robert Gibbs said the officials were watching the situation and that the top priority was for the crew's safety.
"It's a very significant foreign policy challenge for the Obama administration," said Graeme Gibbon Brooks, managing director of the British company Dryad Maritime Intelligence Service Ltd., according to the Associated Press. "Their citizens are in the hands of criminals and people are waiting to see what happens."
Eight ships were hijacked in the Gulf of Aden in the first three months of 2009, according to Reuters. The gulf connects the Indian Ocean to the Red Sea. After pirates seized dozens of ships in 2008, international navies sent ships to the area to reduce the number of attacks.
Last year pirates seized a Saudi tanker carrying $100 million of crude oil and demanded ransom. The crew and ship were released in January after $3 million was parachuted onto its deck.
Many pirates are based in Somalia's semi-autonomous Puntland region. They are typically armed with automatic weapons, rocket launchers and grenades and equipped with satellite phones and GPS equipment. Being a pirate is a high-paying opportunity in Somalia, a county that has lacked a stable central government since 1991.
The pirates operate off mother ships far out to sea and use speedboats to capture their targets. When a ship is seized, they will dock it off the Somali coast while ransoms are negotiated.
In December 2008, the United Nations passed a resolution authorizing military forces to pursue pirates that go ashore in Somalia.