Police are negotiating with a gunman holed up in a farm house west of Brisbane after one their colleagues was shot dead, leaving his family "devastated".

Senior Constable Brett Forte was killed and others received minor injuries after a "wanted man" evaded police in a traffic stop in the Lockyer Valley just before 2pm on Monday.

"We have a person contained and at my last advice we were negotiating with that person," Police Commissioner Ian Stewart said at a press conference on Monday night.

He said police were continue working to resolve the stand-off "as peacefully as humanly possible" following the father of two's death.

"As you would well imagine, the whole family is devastated. Both his own family, the family of his wife and their extended family," the commissioner said.

"We've lost a fine son today."

The respected policeman served with the Queensland Police Service for more than 15 years and was part of Toowoomba's Tactical Crime Squad.

A police source says the wanted man, who is believed to be armed with a machine gun, got out of his car during the chase and shot the officer before driving down a dirt road at Seventeen Mile, just northwest of Gatton.

It's understood another police vehicle rolled over after the chase resumed and the offender also fired at a police helicopter while entering the farm house.

The gunman was holed up in a farm house inside a locked-down area and in a siege situation with Special Emergency Response Team officers at sunset and remains contained within the exclusion zone.

In a tragic coincidence, his death comes on the anniversary of slain Gold Coast detective Damian Leeding's shooting after he responded to an armed robbery at the Pacific Pines Tavern in 2011.

Queensland Premier Annastacia Palaszczuk sent condolences to the slain officer's friends and family and said members of the public should be "immensely grateful" for the work of the police force.

"Every day, the brave officers of the Queensland Police Service put their lives on the line when they go to work," she said in a statement, with Police Minister Mark Ryan calling him "a hero".

Queensland Police Union president Ian Leavers, who knew the late senior constable and described him as a decent person and family man, said the loss was a tragedy.

"One of our colleagues was murdered this afternoon by simply trying to apprehend an offender," he said.

Meanwhile, a single floral tribute has been laid outside the Toowoomba Police Station following Monday's fatal shooting.

Police declared an emergency situation near the Lockyer State Forrest shortly before 4pm and locked down a large area encompassing Fords Road, Forestry Road West, Sandy Creek Road, Gerard Lane, Seventeen Mile Road, Wallers Road and Forest Road.

Local man Terry Hayden told reporters the shooting occurred near his front yard, shaking up his wife who was locked inside.