People in bushfire risk areas were encouraged to leave.
But everybody should be aware of the conditions, Mr Johnstone said.
"People on the land are probably aware of the hot conditions and are prepared for it," he said.
"But it's the bystanders and the other people, that are actually travelling through that, need to be aware of the situation.
"We need people to get out of the way of the fire appliances so those appliances can get to the job really quickly, without being obstructed."
Winds, thunderstorms
Senior BOM meteorologist Dean Narramore said a couple of dangerous days were ahead.
"We could also see some isolated thunderstorms as well, with gusty winds, and they could also act as a source of fire as well," Mr Narramore said
"It's been pretty dry over the last few months and now we're starting to see the air heat up across much of inland Australia.
"Very dry air is leading to these very high, extreme to catastrophic, fire dangers through parts of the Darling Downs, and Maranoa and Warrego."
On high alert
Acting Queensland Premier Steven Miles said he had the utmost confidence in emergency services but the extreme conditions would provide an immense challenge.
"We are well prepared and we're incredibly well served by our fire service, our rural fire service and our volunteer firefighters," Mr Miles said.
"But we have vary rarely seen conditions as optimal as they are right now for fires so that means all of our firefighters, our first responders, they're on alert and prepared for what may come.
"They have done as much back burning as can possibly, and safely, be done to prepare but parts of the state are very dry, they have incredibly high fire loads.
"Keep an eye out for alerts and warnings and heed those warnings and do as recommended."
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