From March 27, Singapore Airlines doubled its frequency on the route between Singapore and HCMC to 21 weekly flights.
Earlier, the carrier operated 11 weekly flights between the two cities.
In addition, it also resumed air services between Singapore and Da Nang, a popular tourist hub in central Vietnam, with seven flights a week. The first flight landed at Da Nang International Airport on Sunday.
Doha-based carrier Qatar Airways announced it will increase the frequency on its route connecting Doha and HCMC to five flights a week from April 12.
It currently operates three weekly flights from Doha to HCMC and Hanoi each.
Vietnam gave foreign tourists quarantine-free entry from March 15 after nearly two years of border closures.
Foreigners entering Vietnam only need to furnish a negative Covid-19 test certificate.