Immigration chiefs sent back the first batch of right-of-abode seekers from the mainland yesterday - 12 days after the Court of Final Appeal ruling that ordered them out.
And officials hinted they might take action at any time to arrest and deport about 1,000 overstayers not involved in ongoing litigation.
'We have a phased deportation plan and we do not rule out that we would go out, arrest and deport them,' principal immigration officer Leung Ping-kwan said.
He said the targeted overstayers were supposed to report to the department within two weeks from yesterday.
A total of 47 overstayers were supposed to report yesterday. Nine failed to turn up.
Nineteen were voluntarily sent back and 11 who refused were detained. Attempts to persuade the other eight to return were being made last night.
Mr Leung said officials took action yesterday because only 162 of the 1,000 overstayers left the SAR after the December 3 ruling, which requires right of abode applications to be submitted in the mainland.
According to department figures there are still about 5,000 overstayers in Hong Kong.
Mr Leung promised that about 4,000 overstayers challenging the reinterpretation of the Basic Law by the Standing Committee of the National People's Congress would not be sent back before the end of the case.
One 48-year-old overstayer said she would continue to stay, though she was not involved in the court case.
'It is unfair to divide us by the criteria of having involvement in a court case or not,' she said.