Four teenagers, including one on bail, were arrested after police on patrol in Gungahlin were confronted by a 14-year-old boy with a knife on Saturday night.

At about 7.25pm, a police foot patrol was alerted to two teenage boys allegedly carrying knives.

As officers approached them, one boy was seen placing a knife under a rubbish bin, while the other allegedly moved towards police holding a knife. He was directed to drop the weapon and complied.

A 14-year-old boy and a 17-year-old boy were arrested at the scene.

Two girls, aged 13 and 14, also engaged with officers during the arrests and were later taken into custody at a nearby store after allegedly stealing items and breaching banning notices.

The 14-year-old boy has been charged with two counts of possessing a knife without a reasonable excuse, while the 17-year-old boy has been charged with breaching bail conditions.

Police say enquiries into the alleged theft offences involving the two girls are continuing.

Anyone who witnessed the incident should contact police on 1800 333000, or via the Crime Stoppers ACT website.