South Korea says the number of new coronavirus cases in the country has more than doubled in one day.
Officials said on Saturday that 229 new cases had been confirmed since Friday, raising the total to 433.
Vice Health Minister Kim Gang-lip said the outbreak had entered "a serious new phase".
Many of the new cases are linked to a hospital and to a religious group near the south-eastern city of Daegu, authorities have said.
Two patients in South Korea have died so far and there are fears the number will rise.
Daegu and nearby Cheongdo - where the hospital is situated - have been declared "special care zones" and the streets of Daegu are reported to be largely abandoned.
The latest developments came as Chinese health authorities reported a decrease in deaths and new cases of the coronavirus on Saturday.
The head of the World Health Organization (WHO), Dr Tedros Adhanom Ghebreyesus, has expressed concern at the number of new cases with no clear link to China or other confirmed cases.
He warned that the window of opportunity to contain the virus was "narrowing".
China has reported 76,288 cases including 2,345 deaths, while more than 1,200 cases of the virus have been confirmed in 26 other countries and there have been eight deaths, the WHO says.
A cruise ship, The Diamond Princess, has been quarantined off the coast of Japan with more than 600 confirmed cases of the virus.
An evacuation flight carrying 32 British and other European passengers has taken off from Japan and is due to land in England later on Saturday.
On Friday, doctors in Italy said a 78-year-old man became the first person in the country to die from the new coronavirus, Ansa news agency reports.
Earlier Italy had announced 16 more cases and its health minister said schools and offices would be closed and sports events cancelled in the affected regions.
The new virus, which originated last year in Hubei province in China, causes a respiratory disease called Covid-19.
What has happened in South Korea?
Medical officials first announced 142 new cases on Saturday and then hours later increased the number by 87.
In a statement, the Korea Centers for Disease Control and Prevention (KCDC) said that of the 229 new cases, 95 were related to Daenam Hospital in Cheongdo. There are now 114 confirmed cases at the hospital - nine staff and 102 patients - it added.
A 63-year-old man died at the hospital on Wednesday and another patient died on Friday in Busan after being transferred from Daenam Hospital, Yonhap news agency reported.
KCDC said 62 new cases - 231 in total - were connected to a Christian sect in Daegu called the Shincheonji Church of Jesus.
Authorities have highlighted that a large number of sect followers attended the funeral of the founder's brother from 31 January to 2 February.
The agency said it had placed 9,336 Shincheonji members in self-quarantine and that, of those, more than 500 were being tested for the coronavirus.
The sect, which has been accused of being a cult, said it had now shut down its Daegu branch and that services in other regions would be held online or individually at home.
At a news briefing, Mr Kim expressed optimism that the outbreak could be contained to the region around Daegu.
"Although we are beginning to see some more cases nationwide, infections are still sporadic outside of the special management zone of Daegu and North Gyeongsang Province," he told reporters.
What about China and elsewhere?
The virus has now hit China's prison system, with more than 500 inmates confirmed infected.
They include 230 patients in a women's prison in Wuhan. More cases have been found in a prison in the eastern province of Shandong and the south-eastern province of Zhejiang.
Some 36 people at a hospital in Beijing have also tested positive.
Senior officials have been sacked for mishandling management of the outbreak.
Passengers of the Diamond Princess who have tested negative continue to disembark the ship in Yokohama after more than 14 days quarantined on board.
However, 18 American evacuees from the ship tested positive after arriving in the US, officials said. More than 300 other US nationals have arrived back in the US after disembarking.
More than 150 Australian passengers have been evacuated from the ship and have already arrived in Darwin, where they will begin two more weeks of quarantine.
Australian officials said on Friday that six people had reported feeling unwell on arrival in Darwin and were immediately tested. Two of those people tested positive despite having received negative tests before leaving Japan.
The first batch of people from Hong Kong have also flown back to the city, where they will similarly be quarantined.
