A man is in a critical condition after being shot in the head and arms by police investigating a theft of a trailer and mower in Brisbane's south-east.

Two police officers went to an acreage on Priestdale Road in Rochedale about 8.40am (AEST) to find the trailer, which was fixed with a GPS tracker.

The senior constables thought there was no one in a four-wheel-drive on the property, but it allegedly started coming towards them with the trailer in tow, police union president Ian Leavers said.

"It took them by surprise," Mr Leavers said.

"They were in fear of their lives and they have used their firearms to protect themselves.

"Both officers acted instinctively as they are trained to do."

The 29-year-old driver was shot in the head once and arms four times and is undergoing surgery in the Princess Alexandra hospital.

The male passenger was not injured and was taken into custody.

Mr Leavers said one of the senior constables was hit by the car and had minor injuries.

"This was just a routine inquiry that suddenly turned as policing does," he said.

"This will live with them for a long time and they won't get over this quickly.

Police and emergency services at the scene of a shooting in Rochedale. ( AAP: Tracey Ferrier )

"Let's say they are experience and competent police."

The constables, from the Logan district, were being interviewed separately.

Acting Assistant Commissioner Stephen Hollands spoke at the scene and said Ethical Standards Command and the Crime and Corruption Commission are investigating.

"It is certainly concerning that police were in a situation where they had to resort to that use of force," Ass. Comm. Hollands said.