As the doors of planes landing at Beijing's Capital International Airport open, teams of security officers and medical workers in hazmat suits take their positions – temperature guns at the ready.

One by one, passengers arriving from abroad are questioned, examined, swabbed and tested for COVID-19. Then they're whisked off for two weeks of quarantine at a government facility.

"You might bring sickness," officials tell them, as the arrivals are greeted as warily as the virus itself.

And for good reason. Airports are now the front line in China's fight against coronavirus, the main defence against the so-called second wave of infections.

Over the past weeks, virtually all new cases – around 500 – have come from abroad, with just a handful of local infections, down to zero on some days.

In response, China announced Thursday that it is closing its borders to all foreigners, including holders of visas and residency permits, effective as of 12 a.m. local time Saturday.

A statement from the Ministry of Foreign Affairs said it was doing so "in light of the outbreak situation and the practices of other countries."

Italy's death toll more than double of China's

The official number of new COVID-19 cases released by Beijing have been questioned by some experts as overly positive for political propaganda purposes and dismissed by some Chinese who have noticed a decline in testing.

A child eats an ice cream outside an ice cream store on its first day of opening after the lifting of the coronavirus lockdown of Hubei province in Xianning, Hubei, on Wednesday. China is breathing a little easier these days but still bracing for a second wave of the devastating viral outbreak. (Aly Song/Reuters)

Still, they reflect China's greatest fear: a return of the epidemic, bouncing back from Europe, the Middle East and North America, where infections are now almost five-fold greater. There are now almost 450,000 confirmed cases outside China versus almost 82,000 inside, according to the Johns Hopkins University and Medicine Coronavirus Resource Center, which is tracking cases worldwide.

Since the coronavirus outbreak began, more than 3,290 people have died from it in China. In Italy, the current official death toll stands at 8,215 while in Spain it's 4,365.

This second wave that is now occurring in China is a lesson for other countries that the battle against coronavirus might not result in a complete victory until it is eradicated everywhere.

On the streets of Beijing, the realization means returning Chinese and foreigners are treated with growing suspicion and increasingly avoided by locals. Many hotels won't take bookings from non-Chinese.

A worker in protective suit delivers meals at a hotel being used as a centralised observation and quarantine site for people arriving in China from overseas. (China Daily/Reuters)

"We must absolutely not let our guard down," a 66 year-old man who called himself Mr. Cao told the Reuters news agency.

Echoing official statements, he said he worries about a rebound in infection numbers and said China must not "put to waste the achievements we've made and the battles we've won."

Wuhan quarantine to lift April 8

China has been celebrating its triumph, lifting an unprecedented two-month lockdown of the key province of Hubei Wednesday and planning an end to the quarantine of its main city, Wuhan, on April 8.

This is the centre of the original outbreak and an area that saw tens of millions of people restricted to their houses —sometimes locked in with padlocks — for weeks at a time.

Apart from one case in the city of Wuhan reported this week, Hubei has no new confirmed COVID-19 cases, government officials in Hubei said Tuesday.

Wuhan has started to loosen the restrictions on movements of residents deemed virus-free, allowing them to leave their homes to conduct personal errands, the Guardian reported.

A man exercises at a riverside park by the Yangtze River in Wuhan Thursday. Life in the city is slowly getting back to normal, but people won't be able to leave the city that was the epicentre of China's coronavirus outbreak until April 8. (Stringer/Reuters)

Medical workers celebrated

Across the country now, portraits of medical workers light up skyscrapers, their sacrifices honoured with ceremonies, gifts and awards. Doctors who were initially silenced by the police for trying to warn about the virus have been officially rehabilitated after being praised as "brave heroes" by China's internet users.

In Wuhan, volunteer nurses and others are cheered and paraded as they fly out, their job declared done.

A nurse in a protective suit feeds a novel coronavirus patient inside an isolated ward at Zhongnan Hospital of Wuhan University during the coronavirus lockdown of city. Nurses and doctors who were once silenced for warning about the coronavirus are now being celebrated. (China Daily/Reuters)

"Now, we are returning home," one medical worker told Reuters.

"So, I'm really excited as we won the victory over the epidemic!"

Recovered patients are applauded as well – a total of 61,000 who overcame the disease just in Hubei – and are featured on state TV receiving flowers and gifts.

The situation is considered so much better in China than elsewhere, wealthy Chinese have even been paying more than $20,000 US for seats on chartered private jets to bring back — sometimes via Canada — their children who are studying in the United States as scheduled flights are blocked or cancelled.

With U.S.-registered planes banned from landing in China and Chinese planes kept out of American airspace, the operation is complicated but still appealing.

"We have arranged a number of private jets traveling from the U.S. to China repatriating Chinese nationals with routes including New York and Boston to Shanghai, San Jose to Hong Kong and Los Angeles to Guangzhou," said Glenn Phillips, a public relations manager at Air Charter Service.

A flight attendant wearing a face mask to prevent the spread of COVID-19 takes body temperature measurements of passengers with a thermometer on a Shanghai Airlines Wednesday. China is being cautious with travellers from abroad, fearing another coronavirus outbreak. (Aly Song/Reuters)

'Premature to celebrate'

Still, experts warn all of this may be too optimistic.

"For China, I think it's too premature to celebrate," said Benjamin Cowling, the head of the epidemiology department at the University of Hong Kong. "There will be a second wave; it's unavoidable."

How big a wave? That depends how successful Chinese officials are at catching the first cases, Cowling said. Aside from testing at borders, they need to track silent carriers, those who don't show obvious symptoms but can spread the virus.

"In China, it's a little easier because of the population surveillance systems," he said. "When someone is infected, officials can go back and see exactly who that person met, like detective work."

China is celebrating victory over the virus, but life is still far from normal. The normally tourist-packed historic district of Beijing, for example, was nearly empty on Thursday. (Thomas Peter/Reuters)

But the virus is spreading faster than expected, says Kenji Shibuya, a public health expert at King's College in London and a former chief of health policy at the World Health Organization,

"Unless you shut down all the borders, you will still have a risk everywhere," he said.

In the end, he said, the only way to stop successive outbreaks — third or fourth or fifth waves — is for all societies to develop what's called herd immunity, and that's only possible after 60 to 80 per cent of the population have had the disease — or once there is a vaccine.

China's second wave is likely only the beginning.