OFFICIALS fear more funds may be needed to cope with the wave of Vietnamese illegal immigrants fleeing China. The cost of keeping the Vietnamese is estimated to be more than $2.5 million a month and officials doubt that repatriation will start before the funds, allocated to Chinese illegal immigrants and Vietnamese boat people, are exhausted. Marine police yesterday intercepted another three boats with 127 Vietnamese, bringing the arrivals this month to 1,074. A Security Branch spokesman said yesterday they might have to seek supplementary funding, although they should have enough for the next two to three months. The need for extra funding would depend on how quickly China responded to requests for repatriation. The spokesman said they had not received any reply from Chinese authorities. The influx has forced the Government to clear lower Chi Ma Wan detention centre and reopen the Kai Tak transit centre to accommodate the Vietnamese. With the rate of arrivals, the 2,000 places are likely to be filled soon. Investigations indicated the immigrants did have household registrations in China, but their permanent residence might not be in Beihai, Guangxi. It was reported the migrants had fled Beihai after their houses were demolished. A source said that as their permanent residence was not in Beihai, the local government did not have a responsibility to take them back. ''China should take these illegal immigrants back because they genuinely come from the mainland, no matter which place they are from,'' the source said.