CBS News reporter Barnaby Lo said the crew members taken captive on the vessel were all Filipino, according to the Philippines' Department of Foreign Affairs. The figure would bring to at least 80 the number of Filipino seafarers currently held captive by Somali pirates.
The ship was en route to Kenya when it was attacked off Somalia's eastern coast, said Noel Choong of the International Maritime Bureau.
He said the latest incident showed that Somali pirates, who were previously operating off the country's northern coast in the Gulf of Aden, have to begun to attack ships in the east.
A multinational naval force patrolling the area has been informed, and ships have been warned to stay clear of Somalia's coast, he said.
"We advise ships to stay at least 250 miles from the coast and even then, they must maintain a strict watch," Choong said.
The latest incident brings to 55 the number of attacks on ships off the coast Somalia this year, most of which occurred in the Gulf of Aden. The surge of attacks has prompted the U.S. Naval Central Command to establish a security corridor patrolled by an international coalition of warships.
The Gulf of Aden, which connects the Red Sea and the Indian Ocean, is one of the world's busiest waterways with some 20,000 ships passing through it each year.
Somalia has not had a functioning government since 1991. Pirates there are often trained fighters, many of them dressed in military fatigues and typically armed with automatic weapons, anti-tank rocket launchers and grenades.