The battle to contain the new coronavirus could take months or even last beyond year-end, a Japanese government panel of experts on communicable diseases warned Monday.

"It may take several months to half a year, or even last beyond year-end" as the virus may survive warmer weather, unlike influenza, Kazuhiro Tateda, a member of the panel and president of the Japanese Association of Infectious Diseases, told a press conference following their meeting.

The panel denied that infections in Japan with the pneumonia-causing virus are increasing explosively. But it also said it is still too early to relax vigilance.

As many large events have been canceled to prevent further infections, the panel said such restraint must be kept up for an additional 10 days.

(Members of the panel)

Also Monday, Japan implemented tougher border control measures on Monday for travelers from China and South Korea, effectively banning tourists from the two countries through the end of this month as part of measures to prevent a surge in coronavirus infections.

Nearly 3 million visas already issued to Chinese and South Korean nationals, also including residents of Hong Kong and Macau, were invalidated. The step, however, will not invalidate the visas of those from the two countries who are already in Japan.

All arrivals from the two countries, including Japanese and other foreign nationals, will be asked to undergo a 14-day quarantine on a voluntary basis.

The travel restrictions came as Japan steps up efforts to contain the spread of the virus with less than five months to go to the Tokyo Olympics. But they will likely deal a blow to Japan's economy as visitors from China and South Korea account for about half of all tourists to the country.

South Korea, angered by Prime Minister Shinzo Abe's sudden announcement late last week of the travel curbs, began taking reciprocal measures on Monday against Japan as ties between the two countries, already frayed over wartime issues, came under new stress.

(Chinese tourists wear masks in Tokyo on Jan. 26, 2020.)

"We did not intend for this to have an impact on Japan-South Korea relations," Chief Cabinet Secretary Yoshihide Suga said at a press conference. "We'd like to carefully explain (to South Korea) our efforts including measures to strengthen border control and prevent further infections, as well as the domestic situation."

China, on the other hand, has accepted Japan's new restrictions as appropriate to safeguard public health.

But on Monday, the Chinese Foreign Ministry said it has decided to temporarily suspend its 15-day visa waiver program for Japanese tourists from Tuesday, as the nation now takes steps to prevent an influx of the new coronavirus from Japan.

The ministry said it has notified the Japanese Embassy in Beijing of the latest decision, adding that Japanese citizens who visit China for business or to meet with their kin will continue to be exempted from visa requirements.

Under Japan's scheme, people entering the country from China and South Korea will be asked to travel to and stay at designated facilities such as hotels at their own expense -- or at their own homes if they live in Japan -- where they will be quarantined for 14 days, and to avoid public transportation and use private cars.

The voluntary quarantine will also apply to those who enter Japan from China or South Korea through connecting flights from another country.

(Fewer people are seen than usual at a departure lobby of Narita airport near Tokyo on March 8, 2020.)

While Chinese and South Korean visitors already in Japan will not have to leave earlier than planned, if they depart the country they will not be able to re-enter using multiple-entry visas while the visa nullification is in force.

A visa-waiver program covering 90-day short stays by tourists from South Korea, Hong Kong and Macau has also been suspended, while airlines will limit flights from China and South Korea to two airports -- Narita, east of Tokyo, and Kansai in Osaka Prefecture.

Of the roughly 3 million visas invalidated, about 2.8 million are for Chinese and about 17,000 for South Koreans, according to the Foreign Ministry.

On Monday, flights heading to Japan from Chinese and South Korean airports were scarce.

Around 8 a.m. at Narita airport, eight passengers from the first flight to arrive from Seoul had their temperatures checked by officers clad in protective gear.

A man in his 40s, who had gone on a trip to South Korea with his wife, said the couple would stay at home for two weeks. "We don't know whether we can lead a normal life. What are the conditions to self-quarantine?" he asked.

Two university students who arrived at Kansai International Airport after a trip to South Korea said their flight was mostly empty, with only three passengers aboard.

(A passenger fills a document at a quarantine counter at Narita airport near Tokyo after arriving from South Korea on March 9, 2020.)

"I was worried about whether we would be able to enter (Japan)," said Wakaba Suganami, 19. "I wouldn't have thought the situation would become as serious as it has."

Opposition party lawmakers, who slammed Abe for what they called his relaxed initial reaction to the spread of the novel coronavirus, and some health experts have questioned the effectiveness of the quarantine measures since they are voluntary.

The virus was first detected in the central Chinese city of Wuhan late last year has spread globally with over 100,000 infections confirmed so far. China has more than 80,000 reported cases of infection, by far the largest, and South Korea over 7,000.

On Monday, Abe told a parliamentary session that Japan is also weighing the need to impose travel restrictions on visitors from Italy as the country has seen a sharp jump in coronavirus infections.

"We have been discussing whether to include Italy. We will not hesitate to do so if the need arises," Abe said.

Italian Prime Minister Giuseppe Conte signed a decree on Sunday, putting the Lombardy region that includes Milan and 14 other provinces under lockdown as the total number of cases surpassed 7,300.

Related coverage:

South Korea strikes back by suspending visas for Japanese

Japan to invalidate 2.8 million visas for Chinese amid virus fears

Japan to restrict travel to and from China, S. Korea over virus