HONG KONG, China (CNN)

Mutations of the SARS virus and relapses among patients are puzzling scientists trying to understand the disease, amid a five-fold increase in the number of deaths in the past month.

Doctors at the Chinese University of Hong Kong said there were two forms of SARS present in the hard-hit Chinese territory, which could complicate efforts to develop a diagnosis and vaccine.

"This rapid evolution is like that of a murderer who is trying to change his fingertips or even his appearance to try and escape detection," Dr Dennis Lo said.

Lo added that more research needed to be done to determine if the virus had become more infectious or deadly.

There were ten new cases and nine deaths reported in Hong Kong on Saturday, bringing to 1621 the total number of infections recorded in the former British colony. A total of 179 people have died from SARS there, while almost 900 have been discharged.

Also worrying scientists is at least a dozen cases of SARS relapses among discharged patients. The World Health Organization is set to discuss the issue with Hong Kong authorities on Monday.

The territory's health chief has also admitted Hong Kong did not respond quickly enough to the SARS outbreak. This was because little was known about the disease, Health Secretary Dr. Yeoh Eng-kiong said in a radio interview on Saturday.

Hong Kong authorities have been criticized for being tardy in imposing quarantines on people who might have been exposed to the virus.

However, recent figures in Hong Kong have backed a declaration from the WHO the SARS outbreak had peaked there.

Across the border in mainland China, SARS cases continued to mount.

There were another 181 new cases and 9 more deaths in China on Saturday. Most cases and deaths have been reported in the capital, Beijing. So far around 1,600 people have been infected with SARS and 96 have died from it in China's hardest-hit mainland city to date.

The deputy director of Beijing Health Bureau, Liang Wannian, said on Friday he believed the SARS epidemic "was in a stable period with the upward trend contained [in the capital]," China's official Xinhua news agency reported.

Beijing authorities are hoping isolation may help. They have opened a new 1,000-bed hospital to handle patients with the virus and barricaded some roads as patients were being transferred.

The Xiaotangshan Hospital threw open its doors after more than 7,000 builders worked feverishly to erect the structure in just eight days.

China's central government has also reversed its stance and agreed to allow WHO send experts to Taiwan to assess the SARS outbreak there.

China, which regards Taiwan as a renegade province, has blocked efforts by the island to join the United Nations body as an independent country. Taiwan has complained that its non-membership to the U.N. is behind a lack of response from the WHO to its requests for help against SARS.

Taiwan authorities have reported nearly 100 SARS cases. There were five new fatalities Friday.

Globally more than 400 have died, and more than 6,000 have been infected with SARS.

In other developments:

• Toronto officials insist the disease is under control in the city after no new SARS cases were reported on Friday. The Canadian city has had the largest outbreak of the virus outside of Asia with 140 probable cases and 23 SARS deaths.

• Singaporean authorities have arrested a man who repeatedly flouted home quarantine. The man, who skipped quarantine and went out drinking on two occasions, was jailed in isolation on Friday. Singapore has put in place strict control measures and has recorded 25 deaths out of 203 cases.

• The World Health Organization says laboratory tests for SARS being used in India are inaccurate. So far, India has reported 19 cases of the disease and has quarantined 200 people.