FEARS are growing that poor weather could force the cancellation of the Lunar New Year fireworks extravaganza over Victoria Harbour on Friday night. Technicians and safety experts flown in from the United States are already hard at work wiring more than 12,000 ''bomb shells'' and explosives to centralised computer systems in preparation for what is being billed as the largest fireworks display in theworld. But if the Royal Observatory proves correct in its weather forecast, the whole thing may turn out to be a damp squib. ''Cloudy and humid with some light rain,'' is the bleak outlook predicted for the Lunar New Year holiday. The display, sponsored by the Bank of China, is costing more than $4 million, and will feature fireworks from 10 countries, including China and Japan. The bank is using the event to publicise the release of new Hong Kong banknotes next May. Flowers that will appear on the banknotes, such as the bauhinia and lotus, will blossom across the sky in a section entitled ''a floral celebration''. Other sections are titled ''a salute to Hong Kong'' and ''aerospace dynamics''. But Ron Dickson, a consultant from US-based company Pyro-Spectaculars, said people should keep a careful eye open at the beginning of the show at 8 pm. ''You'll all see something you've never seen before,'' he said, refusing to elaborate. The team in charge of designing the display to see in the Lunar New Year has spent the past six months travelling all over the world looking for ideas. About 2,600 policemen and Civil Aid Services officers will patrol the coasts of Tsim Sha Tsui and Wan Chai to manage the expected 300,000 people attending the half-hour extravaganza, police announced yesterday. The public will be kept away from the open-air footbridge outside the Cultural Centre during the display, police said. There is also a ban on streamers and spray foam. Buffers will be set up to keep the crowd back from the water, but police are not prepared to keep the number of spectators in the venues within specified levels. Kowloon West deputy regional commander Chief Superintendent Wong Leung Kam-shan said that the Cultural Centre footbridge would be closed from 7 pm until the crowd dispersed. ''We've learnt from the Christmas and New Year celebrations that some young people played with spray foam on the footbridge. Some sprayed the foam on to people below,'' Mrs Wong said. Hong Kong Island deputy regional commander Chief Superintendent Lionel Lam Kin added: ''We shall seize the cans and arrest those refusing to heed our warning.'' The spray cans were cited in the Bokhary report on the Lan Kwai Fong tragedy as one cause of the slippery road surface. Mr Lam also said motorists would be charged if they slowed down on the Island East Corridor to watch the display. Star Ferry and Hong Kong Ferry inner-harbour services will be suspended between 7 pm and 9.15 pm.