'One of the reasons the shipping companies are doing this is because they don't feel this hurts their competitive advantage,' said Veronica Booth, a senior project manager at Civic Exchange, which first proposed the charter.

'The shipping lines are by nature transcontinental, so when they go to places like California they have to switch fuel anyway. They see that the global trend is to clean up.'

Ultimately, though, the charter is a gesture of goodwill, with no regulatory teeth to ensure compliance among its signatories. It expires in January, and if the government does not pass new legislation restricting marine emissions by then, shipping companies will go back to burning bunker fuel in Hong Kong.

'The Fair Winds Charter is a start but it's mainly hype,' said James Middleton, chairman of air-pollution concern group Clear the Air. 'The lame-duck government of Hong Kong has done nothing to create an emission-control area, so all shipping passing through here is burning bunker fuel at will and only the charter members switch to ultra-low- sulphur diesel while at dockside.'

Arthur Bowring, managing director of the Hong Kong Ship Owners' Association, which helped lobby for the Fair Winds Charter, said: 'We need regulation. We're frustrated by the lack of action by government.'

Bowring says the government should require all vessels berthed in Hong Kong to switch to low-sulphur fuel. Eventually, he says, the only way to tackle shipping pollution is to impose an emission-control area for the entire Pearl River Delta region, which would require lengthy negotiations with mainland governments.