For once an airline may have wished it was not on-time.

Asiana Airlines flight 729 departed the gate at Seoul Incheon international airport on schedule at 10:10am on February 29, and a few minutes later took off for the 4.5 hour journey to Hanoi. But at 10:30am, Vietnamese authorities notified Asiana that Korean carriers could no longer land at Hanoi. Will Horton reports on Forbes.

Vietnam gave the option to instead divert to Van Don international airport at Quảng Ninh Province, 140km away from Hanoi, the Korean embassy in Vietnam said. Asiana, which does not normally fly to Van Don, decided to cancel the flight and have it return to Seoul. Flight OZ729 landed back at Incheon about two hours after it took off. The flight reached a maximum altitude of 38,000 feet, according to Flightradar24, and it was nearing Shanghai around the time it turned around.

“We believe it is connected with the spread of the new coronavirus,” an Asiana spokesperson told Yonhap. Korea has the most confirmed cases outside of China. Vietnam this past Tuesday banned the entry of Koreans who had been in the city of Daegu and nearby county of Cheongdo, where the coronavirus outbreak is concentrated.

This was not a total ban on Korean visitors, but travel demand is already significantly weakened, evidenced by the Asiana flight having 40 passengers onboard the A330-300, which seats between 275-298.

While the Asiana flight returned to Seoul, Vietnam Airlines and VietJet had their Seoul-Hanoi flights land in Hanoi as planned. Most other Korea-Vietnam flights are cancelled, especially those from Korea’s low-cost carriers. Korean visitors to Vietnam have rapidly grown, lured by inexpensive resorts closer to Vietnam than traditional getaways further in Southeast Asia, like Thailand and Indonesia.

Korean visitors to Vietnam grew by 23% to 3.1 million in the first nine months of 2019, the latest figures available. Vietnam’s central coastal city of Da Nang is especially popular with Koreans. Before the coronavirus, there were upwards of 20 daily flights between Korea and Da Nang. Vietnam was an important market for Korea’s numerous LCCs, and reflects another key destination seeing a sharp drop in demand. Korea’s LCCs were impacted by last year’s travel downturn to Japan and this year’s coronavirus impacting inbound demand from China.

Many countries are imposing entry restrictions and stricter quarantine procedures for travelers from South Korea over coronavirus concerns, foreign ministry data showed Saturday, as the virus is spreading fast in the country, with infection cases topping 3,150.

As of late Saturday, 34 countries are barring the entry of South Koreans and foreigners who have visited the Asian country in the past few weeks, up from the previous tally of 30, the ministry website updates.

According to a report by Yonhap, Malaysia, Lebanon and the Cook Islands in the South Pacific were the latest to enforce the measure. Kyrgyzstan will begin to impose entry bans Sunday, stepping up their restrictions from tougher quarantine procedures.

Forty-one countries, nine Chinese provinces, and the Chinese cities of Shanghai and Tianjin have tougher quarantine processes, most of which require a 14-day mandatory isolation and close monitoring.

Several Eastern European countries have joined the move, including Latvia, North Macedonia and Bulgaria. Angola, Gabon, Albania and Uzbekistan were also added to the list.

Many of these countries have added China, Japan, Singapore and Italy — where major outbreaks of the virus have occurred — on their quarantine lists.

South Korea added 813 additional cases of the novel virus Saturday, bringing total infections to 3,150, with 17 deaths.

Seoul has called for foreign countries to refrain from taking excessive entry restrictions against South Koreans. But the rapid spread of the COVID-19 outbreak is prodding the countries to take action, from restricting entries and issuing travel alerts to reducing flights to and from Korea.

A South Korean plane bound for Vietnam had to return home less than an hour after its takeoff from Incheon on Saturday as the Vietnamese authorities did not allow the plane to land at the airport in Hanoi as scheduled.

The Southeast Asian country is among many others that have banned the entry of people from South Korea’s two southeastern areas — Daegu city and the nearby North Gyeongsang Province, where major outbreaks of the virus have occurred.

South Korea has also issued an advisory asking its citizens to reconsider or delay any planned trip to countries that have imposed entry restrictions, citing the inconvenience or safety issues that may occur.

Early Saturday, Seoul issued a “navy” travel alert, the lowest on a four-level scale, for all of Japan, advising its citizens to take precautions. The Fukushima region is currently under a higher alert following the 2011 nuclear disaster.

Japan has reported at least 900 infection cases from the coronavirus, most of which come from the quarantined cruise ship in Yokohama.