The 39-year-old man had left his car running in a carport next to his Elizabeth Crescent home while he went to brush his teeth about 6am on Tuesday, August 16, Detective Chief Inspector Neil Grey of Queanbeyan Police said.

As the man walked back out to his car he saw the would-be thief reversing his car out of the driveway.

The man struggled with the offender, who fled the scene on foot.

The offender was described as Caucasian, aged in his mid 20s, with a slim build wearing a black hooded jumper and black pants.

Another running car was stolen at Googong less than an hour later.

A 36-year-old Googong man left his silver Holden Cruze sedan running in the driveway of his Hearn Road home while he ducked inside to retrieve something about 6.45am.

He returned to find his vehicle had been stolen.

Detective Chief Inspector Grey said police were investigating whether the crimes were linked.

He warned people against leaving their cars running and unattended.

"There is a temptation during the colder months to leave your car running whilst the windscreen defrosts. Unfortunately it may not be there when you return," he said.

Detective Chief Inspector Grey said the thefts do not appear to be linked to the theft of a Blue Holden Crewman Utility registered in the ACT (YDZ50T) stolen between 1.30am on Sunday, August 14, and 6.20am on Monday, August 15, from Carinya Street.