WUHAN (AFP, REUTERS) - More than 2,600 new cases were confirmed from a coronavirus outbreak in mainland China, health officials said on Saturday (Feb 15), a day after people returning to the capital from holidays were ordered to quarantine themselves for 14 days.

The total of confirmed infections across mainland China was now 66,492 after 2,641 new cases were confirmed, as of Friday, the National Health Commission said.

The death toll rose by 143 to 1,523, it said, with most of the new deaths in central Hubei province and in particular the provincial capital of Wuhan, the city of 11 million people where the outbreak began in December.

National Health Commission official Liang Wannian told a news conference the government would continue to try to contain the spread of virus in Wuhan, which has been under virtual lockdown for three weeks. The commission was focused on lowering the fatality rate and reducing the infection rate, Liang said.

The number of deaths in Hubei rose by 139 as of Friday, 107 of those in Wuhan. A total of 1,123 people in Wuhan have now died from the coronavirus.

The Chinese capital Beijing on Friday imposed a 14-day self-quarantine on people returning to the city from holidays to prevent the spread of the new coronavirus, and threatened to punish those who failed to comply.

It was not immediately clear how the restriction, relayed by the official Beijing Daily newspaper, would be enforced, or whether it would apply to non-residents of Beijing or foreigners arriving from abroad.

China is struggling to get its economy going after the annual Chinese New Year holiday, which was extended for 10 days to help contain the outbreak of the new and highly contagious respiratory virus.

A top Chinese official, in an interview with Reuters, acknowledged that coronavirus was a deep challenge, but defended Beijing's management of the epidemic and lashed out at the "overreaction" of some other countries.

State Councillor Wang Yi, who also serves as China's foreign minister, said China has taken the most rigorous and decisive measures to fight the epidemic, with many efforts going beyond international health regulations and World Health Organisation (WHO) recommendations.

"Through our efforts the epidemic is overall under control," he said.

A WHO-led joint mission with China will start its outbreak investigation work this weekend, focusing on how the new coronavirus is spreading and its severity, its chief Tedros Adhanom Ghebreyesus said.

The mission will also seek more details on how, where and when the more than 1,700 healthworkers infected contracted the new virus, WHO officials said.

The scale of the epidemic swelled this week after authorities in Hubei changed their criteria for counting cases, adding thousands of new patients to their tally. Cases "clinically diagnosed" through lung imaging are now counted in addition to those that have shown up positive in laboratory tests.

The revision added nearly 15,000 patients to Hubei's tally on Thursday, with the WHO noting that cases going back weeks were retroactively counted.

Authorities said 1,716 medical workers have been infected during the outbreak, with six dying from the illness. Most of the infections among health workers were in Hubei's capital, Wuhan, where many have lacked proper masks and gear to protect themselves in hospitals dealing with a deluge of patients.

The grim figures come a week after grief and public anger erupted over the death of a whistleblowing doctor who had been reprimanded and silenced by police in Wuhan after raising the alarm about the virus in December.

A number of trade fairs and industry conferences in China and overseas have been postponed due to transportation curbs and concerns about the spread of the virus.

International Business Machines (IBM) Corp said on Friday it had canceled its participation in the RSA cyber security conference in San Francisco due to coronavirus-related concerns.

"The health of IBMers is our primary concern as we continue to monitor upcoming events and travel relative to Novel Coronavirus (Covid-19)", the company said in a tweet. The event is scheduled to take place Feb 24-28.

Earlier in the day, Facebook Inc said it had cancelled its global marketing summit scheduled for next month, also in San Francisco, over concerns about coronavirus-related risks.

The Mobile World Congress (MWC), the annual telecoms industry gathering in Barcelona, was also canceled after a mass exodus by exhibitors linked to the coronavirus.