A policeman had his front teeth broken in a struggle with one of the two suspects, who tried to destroy evidence by throwing a beaker containing the drug out of a window.

Chief Inspector Antony Wong Yiu-wing of the Narcotics Bureau said it was a small-scale lab that could produce about 400 grams of Ice daily.

'Our investigation found that the syndicate was using the lab to prepare to build a large-scale factory to manufacture illegal drugs,' he said. He believed the finished product was for local consumption.

Police said the lab posed dangers to residents of the seven-storey building, as chemicals used to make the drug could release toxic gas and cause an explosion.

Officers from the Narcotics Bureau began to investigate the syndicate after receiving a tip-off several months ago.

Early yesterday, they lay in wait outside the third-floor flat of the seven-storey building in Portland Street. Officers rushed into the flat when one of the two men came out at about 8.30am. The younger man was a visitor from the mainland.

Initial investigations showed that the kitchen was used to make the drug, according to police. Some of the Ice, in liquid form, was found stored in a refrigerator in the flat.

The two suspects were being held for questioning last night and no charges had been laid.

Chief Inspector Wong said it was the sixth such drug-making centre discovered by police since 2004. Seizures of Ice rose sharply this year. Police seized 23kg of the drug in the first six months of the year, up from 5kg in the same period last year.