Fast food stores warned after robberies

Fast food workers at four outlets in Brisbane's southside have been left shaken by a series of armed robberies.

The crime spree began on Sunday night when a man and two women armed with a firearm and knives hit a burger joint in Springfield, Ipswich.

They threatened the workers and stole cash before making off in a stolen 2003 white Ford Falcon utility with registration number 120-FG7.

On Monday night, the same group stole cash from three more fast food stores in Rocklea, Salisbury and Algester.

The utility was later found dumped in Heathwood.

"These are fast food outlets where we have young staff going about making a living. They are all traumatised and shaken by what occurred," Acting Detective Inspector Mick Manago said on Tuesday.

"We've increased patrols at all fast food outlets throughout the South Brisbane area."

The trio, believed to be three young adults, are now on the run from Queensland police who are warning fast food stores to be extra vigilant in the wake of the robberies.