Legislator Lo Wing-lok expressed concerns that the infection might be further spread when potential sufferers used public transport to reach the clinics.

'The health authorities could give instructions on hygiene issues to those who are using public transport,' Dr Lo said.

He said the cases might be under-reported as people stayed away from clinics for fear of being identified in the press. 'There should be provisions for privacy - otherwise people might be discouraged from going because they won't want their pictures appearing in the press,' he said.

After inspecting one of the designated clinics, the Sai Ying Pun Jockey Club clinic, Central and Western District Councillor Kam Nai-wai suggested the Department of Health provide transport for people who had to report to the clinics.

'This would considerably reduce the chance of infection and ease the worries of people in the neighbourhood,' Mr Kam said.

'At this stage we don't know who is infected so it is all the more important to dispel fears.'

Despite the rising number of new cases, government spokeswoman Rimy Choi said the number of people identified as having had close contact with atypical pneumonia sufferers remained about 1,000.

She said officials had contacted most of them.

'We will continue to call on citizens to seek medical help as soon as they develop any symptom and we hope that these measures will be effective,' Ms Choi said.

Dr Lo said Hong Kong last implemented a quarantine during a cholera outbreak in the early 1960s, when sufferers were made to stay at a quarantine camp for treatment.

But he doubted that compulsory residential quarantine camps were necessary at this stage and said current measures should be enough to stop the spread.

'Close contact' is defined as people who have cared for, or lived with, a victim, or those who have had contact with that person's body fluids.