Two more people died from the new coronavirus in Iran, infections nearly doubled in South Korea and clusters surfaced in Chinese prisons on Friday, rekindling concerns about an epidemic that has killed more than 2,200 people in China.

The World Health Organization warned nations could face a serious problem if they fail to "hit hard now" against the virus, which has infected more than 75,000 in China and over 1,100 abroad.

China has pointed to official figures showing new cases slowing this week as evidence that its drastic containment measures are working, but fresh infections emerged at two Beijing hospitals, and more than 500 others were reported in prisons across the country.

Chinese authorities have placed tens of millions of people under quarantine in hard-hit central Hubei province, restricted movements in other cities far from the epicentre, and closed schools nationwide.

Many nations have banned travellers from China and airlines have suspended flights to and from the country.

But clusters and outbreaks continue to emerge, and 13 people have now died outside mainland China.

South Korean sect

Iran's health ministry reported two more deaths among 13 new cases of coronavirus in the Islamic republic, bringing the total number of fatalities to four and infections to 18.

Earlier cases had already prompted Iraq to ban travel to and from its neighbour and Kuwait's national air carrier to suspend flights.

Seven of the new cases were in the Shiite holy city of Qom, four in Tehran and two in Gilan, health ministry spokesman Kianoush Jahanpour said on Twitter.

He did not say anything about the suspected source of the outbreak in Iran.

In South Korea, the number of cases nearly doubled to 204, making it the hardest-hit country outside China.

More than 120 members of Shincheonji Church of Jesus, a religious sect in the southern city of Daegu, have now been infected.

It started with a 61-year-old woman who developed a fever on February 10 but attended at least four church services before being diagnosed.

The mayor of Daegu -- South Korea's fourth-biggest city, with a population of over 2.5 million -- has advised residents to stay indoors.

Most people on the streets were wearing masks Friday, but many businesses were closed and workers sprayed disinfectant outside the church.

"With so many confirmed cases here I'm worried that Daegu will become the second Wuhan," said Seo Dong-min, 24, referring to Hubei's capital, where the virus first emerged.

Two Australians evacuated from the Diamond Princess cruise ship, meanwhile, tested positive for coronavirus on their return home despite being cleared in Japan.

An Israeli also tested positive upon returning home -- becoming his country's first COVID-19 case.

The cases will fuel questions about Tokyo's policy of allowing former Diamond Princess passengers to return home after testing negative.

Two former passengers, both Japanese and in their 80s, died in Japan on Thursday.

"If we don't hit hard now using the window of opportunity we might be faced with a serious problem," WHO chief Tedros Adhanom Ghebreyesus said Thursday.

Prisons and hospitals

China reported 118 more deaths on Friday, raising the toll to 2,236, most of them in Hubei.

The National Health Commission also said in its daily update that China tallied 889 new cases, up from the previous day when it reported the lowest number of new infections in nearly a month, fuelling hopes that the epidemic is nearing its peak.

Among those, 258 were outside Hubei, ending a 16-day streak of new infections falling in the rest of the country.

Hubei's figures have raised questions, however, as officials have changed methods of counting cases twice and amended their figures.

Tu Yuanchao, deputy director of Hubei's health commission, said previously removed cases would be reinserted in the tally, acknowledging that the modifications had "created a certain amount of doubt" in society.

A 29-year-old Wuhan doctor died on Thursday, making him one of the youngest known fatalities of the epidemic and the eighth among medical workers.

New hotspots were found in prisons and hospitals.

Seven guards and 200 inmates tested positive for the virus at Rencheng prison in eastern Shandong province. Eight officials were fired over the issue.

In Hubei, 230 cases were reported at the Wuhan Women's Prison, whose warden was also dismissed, and 41 others were reported at a penitentiary in Shayan county. One suspected infection was found at a juvenile detention centre.

Another 34 cases have been found at a prison in eastern Zhejiang province, leading to the ouster of its director and another official.

In Beijing, health officials said 36 people, including medical staff, patients and their families, have tested positive for the virus at Fuxing hospital.

At Peking University People's Hospital, a patient became infected after a visit from two relatives who tested positive for the virus.