The grass fire broke out opposite Kmart plaza during the busiest hours of the day for shoppers.

A Queensland Fire and Emergency Services spokeswoman said they did not know what ignited the fire which grew to about 10 by 5 metres.

The flames engulfed the dry grass which turned into an intense blaze by the time fire crews arrived.

The spokeswoman said the blaze was burning in an "inaccessible" area, and firefighters were working to control the flames.