CANBERRA, Jan 6 (Reuters) - A search is underway in the frigid Southern Ocean for a Japanese sailor reported missing from a whaling vessel, according to media reports on Tuesday.

Hajime Shirasaki, a 30-year-old engine room oiler, was reported missing from a whale spotting ship early on Monday when he did not turn up for his shift.

"There has been a thorough on-board search of the Kyoshin Maru No.2 and when no sign of him was found the sea search intensified," Glen Inwood, a spokesman for Japan's Institute of Cetacean Research, told Australian state radio.

Japanese whaling ships in the area and crews from the New Zealand coast guard were on their way to assist the search, as it was likely Shirasaki had fallen overboard during heavy swells and freezing conditions in the area, Inwood said.

Maritime New Zealand's Rescue Co-ordination Centre said the area was too distant for an aerial search, while conditions in the area meant it was unlikely the sailor was still alive.

"Survival time in waters of zero degrees and a four metre swell is estimated at one hour," centre spokeswoman Christl McMillan told the Sydney Morning Herald.

The search for Shirasaki is the latest in a series of woes to beset the fleet in recent years. In 2007 one sailor was killed in an accident aboard the factory ship Nisshin Maru, while another crewman was killed in an onboard fire on the same ship. (Reporting by Rob Taylor, editing by Jonathan Standing)

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