South Korea has recorded its largest rise in coronavirus infections in a single day, with 594 new cases confirmed on Friday.
The increase brings the total number of infections in South Korea to 2,931, according to the Korea Centers for Disease Control and Prevention (KCDC).
Sixteen people have died in the country so far.
South Korea has the highest number of confirmed cases outside China where the outbreak started.
Separately, there has been concern over a new cases of unknown origin in the US states of California and Oregon, reports the BBC.
What's happening in South Korea?
Most of the Covid-19 cases were in Daegu, the city in the south east of the country which has been at the centre of the country's outbreak.
The spread of the virus in South Korea has been linked to the fringe Christian group Shincheonji Church, seen by some as a sect. Authorities believe members infected one another during services in Daegu and then fanned out around the country, apparently undetected.
South Korean health officials believe that a 61-year-old member of the sect who last week tested positive for the virus was among the first to be infected and is now at the centre of their investigation.
The female patient initially refused to be transferred to a hospital to be tested and is known to have attended several church gatherings before testing positive.
Any large gathering in a confined space she would have attended - like a church service - would have likely led to further infections, health officials say.
The church says it is being unfairly targeted for criticism and has complained of a witch-hunt.
Why are the new US cases of concern?
Authorities in California confirmed the second case in the US of a person who contracted coronavirus, despite not having travelled to an affected area or having had contact with a known case.
The patient has not been identified but has been described as an adult woman with chronic health issues.
Shortly afterwards, health officials in Oregon confirmed a third US case similar to those highlighted in California, described by US officials as community-transmitted cases.
According to figures from the World Health Organization (WHO) for Friday, there have been 59 confirmed cases of coronavirus in the US.
An anonymous whistleblower at the Department of Health and Human Services earlier complained that government workers interacting with quarantined Americans were not provided with proper safety gear, and were allowed to come and go from the secure zone freely.
US health chief Alex Azar has denied the allegations.
The latest developments came as the WHO on Friday upgraded the global risk of the outbreak to its highest level.
But the UN body said there was still a chance of containing the virus if its chain of transmission were broken.
WHO head Dr Tedros Adhanom Ghebreyesus also stressed that fear and misinformation were the biggest challenges to overcome.
What other developments have there been?
- More than 50 countries have now reported cases of coronavirus.
- More than 83,650 cases of coronavirus have been confirmed globally, the vast majority of them in China, where 78,961 people have been infected and 2,791 have died.
- Belarus, Lithuania, Netherlands, New Zealand, and Nigeria all reported their first cases
- The first British death from Covid-19 was announced - a passenger on the Diamond Princess cruise ship docked in Japan
- Fear about the virus has continued to hit global markets. Shares have shed almost 13% of their value this week on London's FTSE, wiping £210bn ($267bn) from the value of companies on the index
- Sources within Iran's healthcare system told BBC Persian that, as of Thursday evening, at least 210 people had died from the virus. This is more than six times higher than the official government figure.
