Firefighters have extinguished a blaze at Warwick East State School on Queensland's Southern Downs, one of the oldest schools in the state, with a building that dates back to the 1850s.

The fire broke out in one of the classrooms on Friday afternoon.

All students and staff have been accounted for and there have been no reports of injuries.

Police Sergeant Shane Reid said three staff members and a child were inside the building when smoke was detected, but were safely evacuated.

It was lunchtime and the school's 260 pupils were moved onto the oval.

Sergeant Reid said by the time emergency services arrived, flames were "leaping high from the roof".

An administration office, two classrooms and a computer lab have been destroyed.

"The scene will be guarded overnight with fire investigators from Brisbane attending tomorrow morning to continue investigations as to the cause," Sergeant Reid said.

The fire broke out in one of the classrooms on Friday afternoon. ( Supplied: David Kemp )

'Roaring out the window'

Resident Morris Monckton was driving back to work when he spotted smoke spewing from the window of one of the classrooms.

He said he was surprised at how quickly the fire took hold.

"It was a matter of minutes — by the time we pulled up and got back, it was roaring out the windows all the way around," Mr Monckton said said.

"It looked like a teacher running around with a garden hose trying to get there … but the heat was across the road, so you couldn't do anything anyway.

"I was surprised how quick it got as big as it did."

Nine-year-old student Phil Hale said he was upset about the fire, but had been 'brave'. ( ABC News )

Mr Monckton said a group of children had already been evacuated onto the oval.

Nine-year-old student Phil Hale said although he was upset about the fire, he had not been worried when teachers had to take students to safety.

"I was brave … and I didn't even cry," he said.

"I ran out of the office and to the oval.

"[Teachers] were upset that it [the school] was burnt."

'Community is really upset'

Southern Downs Mayor Tracy Dobie said the school's administration wing was one of Warwick's oldest buildings and a key feature in town.

"The township of Warwick grew up around that school and generations of families have attended that school — it has a wonderful tradition in our town," she said.

"The community is really upset about it — there will be a lot of anxious people around this afternoon.

"It's really lucky that no-one has been hurt of injured as a result of the fire, and I'm sure that over the next few hours and days we'll find out the cause."

A witness said he was surprised at how quickly the fire took hold. ( ABC News: David Chen )

Queensland Education Department spokeswoman Leanne Wright said the fire had come as a shock, but the department would work with the school and community over the weekend to evaluate the damage.

"We will mobilise to get school back to normal as quickly as possible and with least disruption, however we always work under advice from emergency services," she said.

The school is in the eastern suburbs of Warwick on the Condamine River.

Its National School building, one of the original buildings, is heritage listed.

The school was first founded in 1850, before Queensland was a separate colony from New South Wales.