'As two officers approached him, he drew out a 10-inch [25cm] knife and wielded it in front of police,' the assistant border district commander for operations and crime, Superintendent Yu Chi-hung, said.

'Our two officers had to draw out their service revolvers and issued a warning. He immediately dropped his knife and surrendered to police without any resistance.'

The other two men, aged 21 and 25, were arrested when they were stopped by police for identity checks at 10.30pm and 11.05pm near the bus stop. Each was carrying a knife.

'The two Vietnamese men did not try to escape or resist during the arrests,' Mr Yu said.

The trio admitted sneaking into Hong Kong by hiding under the same cross-border truck in Shenzhen. They separated after the truck crossed the Lok Ma Chau border checkpoint.

'The three suspects claimed they came to Hong Kong to carry out robberies ... But we have a strong feeling that the three men sneaked into Hong Kong in the hope of being arrested and going to jail in the city,' a police source said.

'They think living in Hong Kong prisons is much better than their lives in their hometown. When they leave jail, they can get payment for their work in prison.'

The three men were still being questioned by police last night.

Police have arrested about half a dozen Vietnamese illegal immigrants in Lok Ma Chau since the Lunar New Year. Most were carrying a weapon.