The two policemen on board were thrown overboard but managed to swim to safety.

The illegal immigrants, all Pakistani nationals and accompanied by two mainland snakeheads, were stranded when their speedboat ran aground while trying to flee during an earlier police operation. All were eventually rescued and no one was seriously injured.

Police later also nabbed another eight illegal immigrants of Pakistani origin during a follow-up search in Mai Fan Tsui in Sai Kung. The illegals are aged between 20 and 49 while the snakeheads are in their late teens.

Marine police division commander Cheung Mei-hon said the policemen's dinghy sank after it was holed when thrown against sharp rocks by huge waves.

A spokesman said the chase began when the two marine policemen came across a suspicious speedboat at Tuen Tsui near Sai Kung around 11pm on Sunday and gave chase.

While trying to shake off the cops, the speedboat ran into rocks at the foot of a cliff, trapping the two snakeheads and six illegals who were on board.

The marine police's rescue team and the Government Flying Service were called in early on Monday to rescue the stranded men. The police dinghy sank during that effort.

The stranded illegals were eventually rescued around 1pm.

The illegals claimed they had paid 5,500 yuan (HK$6,242) each to be taken from Shenzhen to Hong Kong, where they hoped to apply for political asylum.

Cheung said there were no life vests in the speedboat, and the snakeheads had been reckless in trying to outrun the police in high seas and along a rocky coast. "The masterminds tend to hire young people who used to be fishermen [to drive the boats] because they are familiar with the region."

Police have stepped up enforcement action against illegal immigrants in Hong Kong waters since the Court of First Instance ruled in March that asylum seekers would not be breaching the law if they took up work.