The decision by the Director of Immigration, Lai Tung-kwok, to retire in April has raised concerns about the appointment of a successor.
Although Mr Lai was due to retire in November this year when he turned 57, a government source said Mr Lai wanted to take pre-retirement leave and quit in April.
The Civil Service Bureau confirmed yesterday that it had received Mr Lai's notice of retirement.
It said it would follow standing procedures to appoint a new director and make an announcement in due course.
The director of immigration is one of the principal officials whose appointment and removal has to be approved by Beijing under the Basic Law.
Immigration Staff Association chairman Wong Tong-sing said he was 'a little shocked' to learn that Mr Lai was said to be leaving in April.
'We had heard earlier that his retirement was due by the end of this year,' he said.