Immigration and buildings officials are to increase co-operation to crack down on the problem of illegal workers in the wake of the fatal collapse of a balcony on Sunday. A security source said the Immigration Department would ask the Buildings Department for more information about construction sites or buildings undergoing renovation or demolition work. 'This will allow the officers to have clearer targets [for their anti-illegal workers' operations] and improve efficiency,' the source said. The move follows Sunday's accident in which illegal mainland worker Lai Heung, 33, died instantly when he fell 40 metres after an illegal balcony he was helping to remove from the 12th floor of a residential building in Yuet Wah Street, Kwun Tong, collapsed. His colleagues Yick Sing-mau, 39, and Cheng Lai-kwan, 38, were taken to United Christian Hospital, where one is in serious condition and other is critical. On Monday, a 54-year-old man who allegedly hired the three workers surrendered to police. He was released on $10,000 bail last night. The security source said the Immigration Department would also strengthen ties with private property management companies by training security guards to spot forged identity cards. A total of 5,180 illegal workers were arrested in the first six months this year, compared to 7,841 and 5,715 in the whole of last year and 2000, respectively. Among those arrested, 3,734 were two-way permit holders. The source said 550 illegal workers and employers had been arrested since July alone, resulting in 365 prosecutions, 40 against employers. While the total number of illegal workers arrested had increased, the source said he did not think the problem was out of control. He said the surge was partly due to the increase of mainland visitors and he believed the introduction of smart ID cards would help keep the problem in check. Meanwhile, buildings officers yesterday inspected Yuet Wah Street for other illegal structures. They inspected 96 flats and issued 65 orders for the removal of illegal structures. The inspections will continue for about a week. Buildings Department acting director Cheung Hau-wai urged property owners to appoint registered contractors for the removal of illegal structures. To raise property owners' awareness of building maintenance and the danger of unauthorised structures, the Buildings Department has published a guidebook which provides details of statutory requirements and construction technology. Police arrested 17 mainland illegal labourers and two Hong Kong men in two separate operations in Kwun Tong and Sai Kung yesterday. Four of the 17 men - three visitors and an illegal immigrant - were caught carrying out decoration work when officers raided a flat in Hoi Yuen Road, Kwun Tong. They also arrested two Hong Kong men in the flat who allegedly hired the mainlanders. In the other case, officers arrested 13 illegal workers - mainland visitors - when they raided a housing construction site in Kau Sai new village off Hiram's Highway, Sai Kung. All the arrested were being held for questioning.