At least 52 flights by Vietnam Airlines were canceled, delayed or unable to land at the Noi Bai Airport in Hanoi on Saturday due to heavy fog.
The national flag carrier said that from 8 a.m. on Saturday, it had canceled six flights from Hanoi and changed the landing destinations for six other flights coming in to Hanoi.
Around 40 domestic and international flights from Noi Bai airport were delayed and several flights had to land in airports in nearby Hai Phong City and even Laos, it said.
The airlines said it planned to offer more flights on Sunday if the weather improved.
Low-cost carrier Jestar Pacific Airlines said it had to cancel a flight from Hanoi to Ho Chi Minh City while two flights from HCMC had to land in Hai Phong instead of Noi Bai airport.
As many passenger flights could not leave Hanoi, Jestar said it had to fly empty airplanes to HCMC to serve other routes from the city.
The empty flights and the landing charges cost JPA more than US$10,000, it said.
More than 7,000 airline passengers have been affected by the fog.
Aviation authorities said the fog appears in Hanoi and several northern provinces every year in February and March. This year it had come earlier and was more severe, they added.