The large proportion of sporadic cases 'with no record of previous contacts with Sars patients' casts a shadow over the prospect of controlling the disease in the capital.

But the number of new cases in Beijing dropped to 48 yesterday.

This is the lowest number since the government finally started disclosing daily Sars figures on April 20.

The number of new suspected cases in the city also dropped significantly to 54. Two more deaths were recorded.

There were 118 new cases and six deaths nationwide.

The deputy director of Beijing's municipal health bureau, Liang Wannian, yesterday said Sars was declining in Beijing.

The number of new cases, excluding those converted from suspected cases, dropped by half to an average of 30 to 40 after May 2, Mr Liang said. Beijing recorded an average of 70 to 80 new confirmed cases from April 21 to May 2.

'The rising trend of Sars in Beijing has been effectively controlled and the epidemic is now declining,' he said.

Government spokesman Cai Fuchao said quarantine orders for 895 people had been lifted, including 274 construction workers from an infected site.

So far, the city has put 18,608 people in quarantine and 10,571 people have been released.

But mainland and overseas health experts warned it was too early to conclude that the peak was over.

World Health Organisation director-general nominee Jong-Wook Lee yesterday questioned the government's claim that infections had stabilised.

He said this was very subjective, adding 'we cannot really tell if it's a peak or not a peak'.

Dr Lee, from South Korea, spoke to the media for five minutes during a one-day visit to Beijing to meet Vice-Premier Wu Yi and other health and foreign affairs officials.

He will become WHO director-general in July if confirmed by the World Health Assembly.

Hong Tao, principal research fellow of the Institute of Virology under the Chinese Centre for Disease Control and Prevention, said: 'I dare not make such a conclusion. If they record the same level of new cases for the next 10 days, then I could say the epidemic has been controlled.'

Mangai Balasegaram, spokeswoman for the WHO's Beijing office, said one key unknown in the capital was the large number of cases with no previous contact with Sars patients.

'If you don't know where they contract the disease, you don't know what is happening,' Ms Balasegaram said.

Mr Liang said yesterday Beijing managed to trace the source of only 40 to 50 per cent of infections.

'There are other sources of infections [in addition to hospitals] that we cannot trace,' he said.

'Some people just popped up in the hospitals. There are many reasons for this. We do not rule out that some non-Beijing residents came here for treatment.

'Some have displayed few symptoms during the incubation period and they do not go to the hospital promptly.'