AirAsia's colourful chief executive Tony Fernandes has stepped aside from the company while authorities probe unusual payments at the Malaysian carrier, as the fallout from a $4 billion bribery fine at Airbus reverberates across the industry.

The shock decision came after Britain's Serious Fraud Office (SFO) released details of a probe that found individuals associated with the planemaker had paid to secure deals with AirAsia and its long-haul unit AirAsia X.

Fernandes and executive chairman Kamarudin Meranun said in a statement late Monday: "We are relinquishing our executive roles with immediate effect for a period of two months, or such other period that the companies may deem fit."

They added that they "categorically deny any and all allegations of wrongdoing or misconduct on our part as directors of AirAsia. We would not harm the very companies that we spent our entire lives building up to their present global status".

They will remain with the airline as advisors, they said.

Malaysia's anti-corruption commission said on Saturday it was empowered to investigate any act of corruption committed by citizens or permanent residents anywhere outside the country.

Two other agencies in Malaysia, including the aviation agency and the Securities Commission, reportedly have started their own probe.

Fernandes has been one of Airbus's most loyal customers and his Malaysia-based budget airline, which he bought for one ringgit (25 cents at the current rate) in 2001, is the European manufacturer's largest customer for single-aisle jets.

Airbus is the only plane supplier to AirAsia.

AirAsia shares plunge

The news has sent shares in AirAsia plunging 20.9 percent since Monday following the release of the SFO's investigation, with the price at its lowest since September 2015.

Tan Kam Meng, analyst with local brokerage TA Securities, warned of further losses if Fernandes and Kamarudin are charged.

"If the probe is unfavourable against them or they are charged in court, the impact will be a disaster to shareholders," he told AFP. "I am shocked by the news of the bribery."

The losses have been compounded by a deadly Chinese virus outbreak that has seen several airlines cancel flights to the country, one of AirAsia's most profitable routes.

"It is a double whammy for AirAsia," analyst Tan said.

A French court last week said Airbus had agreed to pay 3.6 billion euros ($4 billion) in fines to Britain, France and the United States to settle corruption inquiries sparked by suspicious equipment sales.

A court document on the SFO website says EADS France SAS -- which was later renamed Airbus Group SAS -- paid $50 million as sponsorship for a sports team owned by two unnamed AirAsia executives.

"Key decision-makers" in AirAsia and AirAsia X allegedly rewarded the firm with an order of 180 aircraft from Airbus.

But in a new statement Tuesday, the pair denied that his former Formula One team was involved in any bribery scandal.

“Caterham F1, the company alleged to have been sponsored improperly by Airbus, was at the relevant time a Formula 1 racing team that had gone round the globe promoting among others AirAsia, AirAsia X, GE and Airbus,” Fernandes and Kamarudin said in the statement. 

“Throughout the period we were shareholders in Caterham, the company made no profit and was eventually disposed of for 1 pound sterling in 2014. From start to finish, this was a branding exercise and not a venture to make profit.”

The flamboyant Fernandes has carved an image for himself as Asia's answer to Richard Branson, shaking up Southeast Asian air travel with his carrier's slogan "Now everyone can fly".

Fernandes and Kamarudin have not been shy in flaunting their wealth and both once owned the now-defunct Caterham Formula One racing team, while they are also majority owners of London football club Queens Park Rangers.