GM stunned Supercars teams and officials on Monday by announcing they were "retiring" the iconic Australian brand by 2021 after plunging domestic sales for Holden vehicles.

Triple Eight operates as Holden's factory team in the Supercars championship, through its Red Bull Holden Racing Team.

The team features former Supercars championship winning drivers Jamie Whincup and Shane Van Gisbergen and is preparing for the season-opening Adelaide 500 this weekend.

Team boss Roland Dane was unable to speak to Holden's interim chairman and managing director Kristian Aquilina as he was travelling to South Australia on Monday.

AAP understands Dane is eager to discuss what the decision means as soon as possible.

"We're incredibly saddened for all Holden employees, dealers and fans and our thoughts are with them at this difficult time," Red Bull HRT said in a statement on social media.

"We'll update RBHRT and Supercars fans with our future plans in due course, but right now we're supporting our friends and colleagues at Holden."

Seven-time driver's champion Whincup, who is expected to make a decision on his own racing future this week, also took to social media to express his disappointment in Holden's decision.

"Nothing will EVER spin the rear wheels like a V8 Holden," Whincup posted.

"Sad day for the Australian automotive industry and my thoughts are with the employees and dealer group."

While Triple Eight's factory deal, which is supposed to run until the end of the 2021 season, is up in the air, Monday's decision affects half the Supercars field.

Seven other teams are set to race Commodores in 2020.

Aquilina said Holden would honour their Australian motorsport commitments this year.

"Our intention is still to go racing in 2020 whilst we've still got Holden vehicles out there in dealer showrooms," he said.

"To the extent, about GM and its involvement in racing beyond that, that will be part of the same conversation."

Australian Associated Press