A firefighter remains in a critical condition after being rescued as crews contained a large blaze south of Brisbane.

A second firefighter was also transported to the Royal Brisbane and Women’s Hospital with serious injuries, after paramedics were called to the Slacks Creek blaze about 2.30am on Tuesday.

Multiple crews were involved in the rescue and one of the injured firefighters required CPR once they were outside the building, Queensland Fire and Emergency Service Deputy Commissioner Michael Wassing said.

“It was certainly during the hottest part of our firefighting operations,” he said.

“It is very rare that our firefighters are injured in this way and that’s because of the enormity of the training and the professionalism of our firefighters.”

The rescue was performed by breathing apparatus safety teams, and there are systems used to alert crews to firefighters’ locations.

“That’s how they effected their rescue,” Mr Wassing said.

Queensland Ambulance responded with “numerous additional units” when the firefighters were injured while trying to control the blaze, medical director Stephen Rashford said.

Crews were called to these types of jobs “quite frequently”, United Firefighters’ Union Queensland’s John Oliver said.

“I just want to know what’s happened in this particular instance,” he said.

Mr Oliver said he was concerned for the injured firefighters and those who rescued them.

“Obviously there’s an emotional toll that goes with that, but I can say they would have done their best efforts and that’s proven to be correct today,” he said.

Internal counselling services are available.

The fire was contained just after 6am. A cause is yet to be determined after police declared a crime scene.

Officers are checking the surrounding area for CCTV and the business owners are speaking with investigators.

Power was interrupted to the premises when a pole was knocked down in the past few days, Detective Inspector Chris Knight said.

– AAP