A Chinese fishing boat with 24 people on board has been seized off the Kenyan coast by "unidentified persons", China's official Xinhua news agency said on Friday.

Xinhua, citing a source in China's transport ministry, said the boat was seized late on Thursday.

"The abductors demanded the Chinese fishing boat sail towards the coastal area off southern Somalia," the report said.

The crew consisted of 15 Chinese, one Taiwanese, one Japanese, three Filipinos and four Vietnamese, it added.

Somali pirates have been causing havoc in one of the world's busiest shipping areas connecting Europe to Asia and the Middle East, taking millions in ransoms, forcing up insurance costs, and threatening humanitarian supplies.

Most attacks have been in the Gulf of Aden between Yemen and north Somalia, a major route leading to the Suez Canal linking Europe and Asia.