The tanker St James Park, which was seized by Somali pirates. Picture: Derek Lilley
The St James Park, which had been sailing to Thailand from Spain, was seized on Monday, Andrew Mwangura of the East Africa Seafarers' Association said.
A total of 26 crew members, of mixed nationalities, were on board the vessel.
A Panamanian-flagged bulk carrier with 19 crew members was also hijacked off the southern Somalia coast on the same day.
The St James Park was carrying a chemical used to make plastics when it sent a distress signal from the Gulf of Aden, Mr Mwangura said.
Noel Choong, of the International Maritime Bureau, said the St James Park sent a distress message late yesterday seeking help from pirate attacks.
He said the call was picked up by a Greek rescue centre that relayed the message to the IMB but the bureau had failed to establish communication with the vessel.
Mr Choong added that the tanker's owner later informed the IMB that the vessel had been seized.
The ship is owned by Zodiac Maritime Agencies of London, which runs 150 vessels and employs more than 5,000 crew.
Operations manager Paul Shields would not confirm if any Britons were on board but added there were not believed to be any casualties.
"We are dealing with an ongoing situation. Our main aim is to get the crew released as quickly as possible," he said.
"So we are going to be very limited in what we say other than that we are working with all the relevant authorities to get the release of our crew."
The capture took place on the same day pirates and maritime officials confirmed the release of Singapore-flagged container ship Kota Wajar and its crew for a $4m ransom.
The release was confirmed by the European Union naval force (EU Navfor) patrolling waters off Somalia.
The 24,637-tonne Kota Wajar was seized on October 15 north of the Seychelles as it was sailing to the Kenyan port of Mombasa from Singapore.
EU Navfor said the Canadian warship HMCS Fredericton was now providing medical and logistical help.
Somali pirates continue to hold British couple Paul Chandler, 59, and his wife Rachel, 55, after their yacht was seized near the Seychelles on their way to Tanzania in October.
Source: SKY News, December 29, 2009