Drivers compete at the Portuguese Grand Prix F1 race on October 25 in Portimao, Portugal. Photo: IC

Formula One unveiled a 23-race calendar for 2021 on Tuesday, its biggest ever, but the Vietnamese Grand Prix has been dropped.

The season will start in Australia on March 21 and will include the first-ever race in Saudi Arabia on November 28 before the season ends a week later in Abu Dhabi.

Vietnam was to hold a street race on April 25 but doubts about the event arose after Nguyen Duc Chung, who was Hanoi's mayor and a major supporter of the event, was arrested on corruption charges in August. In the calendar unveiled on Tuesday, the race slot was left vacant.

F1's 2020 season was heavily disrupted by the COVID-19 pandemic but is eventually being run over 17 races, with reigning champion Lewis Hamilton on course to win the title for the seventh time.

Spectators have been barred from most races this year but organizers said they expect fans to return next year.

"The plans for 2021 have involved extensive dialogue with all promoters and their local and national authorities at a time of ongoing fluidity related to the global pandemic," F1 said in a statement. 

"As we have said before, we expect fans to return for the 2021 season and for the calendar to look similar to the originally planned 2020 season."

Vietnam inked a 10-year deal with Formula One in 2018 with state media saying hosting the race would cost the country $60 million per year.

The fee has been picked up in full by the country's largest private conglomerate, VinGroup, which had been hoping to dazzle with a night race.

But its 2020 race was canceled due to concerns that teams and fans coming from overseas could spark a new outbreak of COVID-19 and the corruption scandal surrounding Nguyen Duc Chung now threatens the future of the event.

Saudi Arabia, with a November 28 night race along the Red Sea corniche in Jeddah, will become the 33rd country to host a Formula One race.

Brazil's race at Sao Paulo's Interlagos circuit on November 14 was subject to a new contract being agreed, as was Spain's round in Barcelona on May 9.

Formula One had planned to move to a new circuit in Rio but that has proved controversial for environmental reasons and work has yet to start.

The Dutch Grand Prix, at Zandvoort, returns for the first time since 1985 with a race on September 5 and immediately after the August 29 Belgian Grand Prix at Spa-Francorchamps. It forms part of a triple-header with Italy on September 12.

Russia, Singapore and Japan will also form a first long-haul triple-header on September 26, October 3 and October 10.