Shipping industry figures fear the resulting higher premiums could upset delicately balanced trade through the strait, which funnels oil and raw materials to China and the rest of North Asia and manufactured goods to Europe.

Flanked by Indonesia, Malaysia and Singapore, the strait remains a hotbed of piracy. But the shipping companies say it is unfair and highly unusual to class it as a war zone.

The Joint War Committee insurers' grouping based in London, whose decisions are generally followed internationally, cited a private defence report that warns of an al-Qaeda attack on a 'significant maritime target' this year.

The report by Aegis Defence Services says global logistics are now so finely tuned 'that any disruption to the delivery of oil or gas to North Asia, or goods whose manufacturing has been outsourced to Asia for sale in Europe, would have fundamental negative economic consequences'.

Arthur Bowring, managing director of the Hong Kong Shipowners' Association, said his group was deeply worried at the impact of the war risk assessment. Members include Cosco, China Navigation and Orient Overseas Container Line, the family firm of former chief executive Tung Chee-hwa. Mr Bowring warned it could hit economies across the region as increased costs inevitably flowed down industry supply chains.

'We are very concerned at the labelling of the Malacca Strait as a war risk. It is, of course, one of the world's biggest economic arteries and therefore this could impact Asia's economies,' he said. 'We need to find valid reasons to overturn the underwriters' move and I'm confident this can be done.'

The association already has made its opposition known through a submission on behalf of the Asian Shipowners' Forum to the International Chamber of Shipping, which met the Joint War Committee in London on Thursday. No fresh decision emerged, apart from a pledge to hold further talks in London in two weeks. The association will represent the forum directly, along with regional governments.

A director of a prominent Hong Kong shipping-sector firm warned that the impact could be huge.

'We are all waiting to see quite how high these premiums are going to go,' he said. 'The Malacca Strait is our lifeline and it is just absurd to describe it as a war zone. It is a sign that the cost of terrorism is really starting to bite.'

The director said the strait was no more a war zone than London or New York.

Daniel Poon Wing-choi, assistant chief economist with the Hong Kong Trade Development Council, said: 'It will add cost to Hong Kong exporters.

'Many of the Hong Kong exporters' products are under threat because their margins are very thin. This, in turn, is due to keen competition in their respective industries. One such industry is the garment sector in Hong Kong, since there are no quotas this year.'