A suspected gunman has held-up a boy in Biggera Waters.

Just after 2pm on Tuesday, the 15-year-old was waiting for a bus on Coombabah Road when he was approached by a man who produced what was believed to be a firearm.

The man then stole the boy's bag containing a mobile phone and other items, before fleeing on foot.

The alleged thief is described as Caucasian, aged in his 20s, approximately 180cm tall with a proportionate build and dark brown hair.

Anyone with information should contact Crime Stoppers on 1800 333 000.