THE high number of illegal immigrants sneaking into Hongkong through Deep Bay in recent years has prompted the Government to consider closing the estuary of Yuen Long Creek. The Government also plans to reinforce a two-kilometre border fence west of the creek. The deputy Secretary for Security, Mr James Morris, said the action was necessary because the number crossing illegally in the first three months of this year was consistently higher than for the same period last year. The number of illegals caught in the territory every month is expected to hit 4,000 this summer - the highest in 12 months. In the first three months, 9,290 were arrested, 40 per cent more than last year's quarterly total. Although co-operation with China was good and illegal immigrants were repatriated upon arrest, Mr Morris said it was difficult to control the influx. ''It is not possible to stop illegal immigrants entirely, but we will keep on co-operating with the Chinese Government to get more information on the routes they come from and persons involved in helping them,'' he said. Mr Morris said the Government planned to close the estuary of Yuen Long Creek although there would be practical difficulties involved, such as finding a way to erect a barrier in the water. ''It was not a problem area before, but it has become one in recent years,'' he said. The problem became apparent as more arrests have been made in that area. For the time being, Mr Morris said the authorities would reinforce the nearby border fence west of Yuen Long Creek all the way to Tsim Bei Tsui, which has been identified by the police as part of the problem. The border fence west of Yuen Long Creek will be upgraded to include a few more layers of heavier meshed wiring similar to that running between Sha Tau Kok and east of the creek. The entire fence from Sha Tau Kok to Tsim Bei Tsui is 34 kilometres long and 3.54 metres high and the one west of Yuen Long Creek is two kilometres long. Mr Morris said the improvements would be made within existing resources. The fence was upgraded in 1989 and $16.5 million was spent under a two-year programme. In addition to maintaining a defensive perimeter at the border, Mr Morris said employers would be discouraged from hiring illegal immigrants by the imposition of heavy fines and constant checks on identity cards. Chief Superintendent Vince Chapman, who heads the field patrol detachment, said the problem of illegal immigrants working at construction sites had almost disappeared since heavy fines began to be imposed on employers. But there was a growing problem of farm owners hiring illegal immigrants. More than 1,000 were caught in farms in Pat Heung last month. ''When you find them [the illegal immigrants], it is impossible to link them to a particular farmer since they will tell you they just happen to pass by the farm and will not admit they work there,'' Superintendent Chapman said. He said it was difficult to stop Chinese illegals from working at farms without the co-operation of the farmers. At the moment, there are 680 staff in the field patrol detachment. Superintendent Chapman described the level of manpower as adequate with about 240 to 250 men deployed for each shift. Seven suspected illegal immigrants were arrested yesterday morning after police found them wandering along Clearwater Bay Road. The three men and four women said they landed in Clearwater Bay by junk shortly before 7 am. They were from Hoi Fung in Guangdong Province, police said. Those arrested were last night detained pending deportation.