EMERGENCY services were on full alert last night after 2,000 Vietnamese migrants staged a mass protest at Tai A Chau Detention Centre over the ''transfer'' of a teenage boy to the Whitehead camp prior to his planned repatriation. Five police launches were sent to the camp and government helicopters were on standby to fly further reinforcements to the island, off Lantau, if trouble erupted. No arrests were made and late last night police officers, led by Chief Inspector David Greenwood, negotiated with senior Vietnamese representatives and persuaded demonstrators to return to their huts late last night. The mass sit-in started just before 4 pm after Ngo Van Ha, 16, was taken from the camp. More than 2,000 protesters blocked the entrance and shouted for his return. The teenager's lawyer was outraged Ha had been transferred. Pam Baker said she had not been informed of the order to move the boy even though she had visited him at the camp just hours before his departure. ''They made no attempt to contact me,'' she said. ''I was in Tai A Chau seeing him until 2 pm and they must have waited until I had gone and then grabbed him.'' Mrs Baker was informed after 11 pm that the protesters were told Ha would be returned to Tai A Chau tomorrow, which she said is why they returned to their huts. She also said she would be seeking a judicial review tomorrow morning in an attempt to block Ha's repatriation. Refugee Co-ordinator Brian Bresnihan said Ha, who arrived in Hong Kong in 1990 and was screened out as a refugee in March 1992, was moved to the departure centre at Whitehead. ''The transfer had been made following a long standing request from the UNHCR [United Nations High Commissioner for Refugees]'', he said. Ha's plight made headlines earlier this month when his uncle and aunt, Nguyen Dang Vu and Ho Thi Phouc Tuyet, who live in California, tried unsuccessfully to have the boy made a ward of court. According to a Government statement last night, the decision to transfer and repatriate the teenager, whose parents were killed in a car accident in Vietnam when he was 10 years old, was for his own benefit. ''Ngo Van Ha had been the subject of guardianship proceedings earlier this month when an application to the High Court to make him a ward of relatives in the United States had been rejected,'' the statement read. ''The UNHCR Special Committee on unaccompanied minors had decided that Ngo Van Ha, who had been determined a non-refugee, should return to Vietnam.'' Mr Bresnihan said: ''Ngo Van Ha's transfer to the departure centre was made to facilitate his repatriation under the family reunion programme.'' Jahanshah Assadi, the UNHCR Chief of Mission, said he was ''satisfied Ngo Van Ha's best interests would be served by his early return to Vietnam''. But in a terse statement to the Sunday Morning Post last night Mrs Baker said: ''This is no way to discuss the future of a child, through the press, but the UNHCR leaves me no alternative. ''They say they have 'reconsidered' - they knew I was getting further information and they have not contacted me. ''There is no home for Ha in Vietnam. A stable, close family exists in California, consistent in their efforts to have this young boy join them and give him a home, they want to welcome him.'' Mrs Baker also said that when she spoke to Mr Assadi after the court case on January 3, he said she could have a further two weeks to collect more evidence. to support the claim of his relatives in the US. Tai A Chau, which was opened on February 25, 1991, holds just over 7,000 Vietnamese boat people, of whom 6,000 have been screened out. The remaining 1,000 are awaiting screening.