A quick-thinking taxi driver caught two Vietnamese illegal immigrants who tried to rob him in Tuen Mun yesterday by trapping them inside his cab. The hold-up occurred after So Shing, 41, picked up the two men outside Tin Yue House in Tin King Estate, Tuen Mun, at about 11.30am. As the green cab arrived at a taxi stand outside Tuen Mun ferry pier in Wu Chui Road, one of the two men pulled out a screwdriver and threatened the driver. But the driver jumped out of the taxi and pressed the central lock button, trapping the two would-be robbers inside the cab. Four other cab drivers who were waiting for customers at the taxi stand were alerted when Mr So shouted for help. The police were then called. 'We stood guard outside the taxi and held the four doors to stop them running out,' Mr So said. 'The two Vietnamese men apparently did not know how to unlock the door. They used their bodies in an attempt to force open the doors but we blocked them from outside.' The taxi drivers held the doors for several minutes until officers from New Territories North Emergency Unit arrived. The two men were then arrested. Officers seized the screwdriver, five rounds of ammunition and a cutter from the suspects. Last night, the two men, aged 39 and 44, were being detained in Castle Peak police station. They were suspected to be among more than 30 Vietnamese men who sailed into Hong Kong on an eight-metre motorised sampan and went ashore in Lung Kwu Tan in Tuen Mun on Sunday. Police arrested 29 of them on the same day in a huge search in Lung Kwu Tan in Tuen Mun, seizing 38 rounds of ammunitions, 13 knives, a hammer and two water pipes. On Monday, three more were caught in Tuen Mun. Some 28 Vietnamese, aged 21 to 53, have been charged with illegally remaining in Hong Kong. Their case was heard in Tuen Mun Court yesterday, although the men are being kept in police detention and did not appear. No pleas were taken and the case was adjourned. In an unrelated case, four Vietnamese illegal immigrants were arrested in Lau Fan Shan last night. Police searched them and found a knife and a pair of scissors.