A boy and a girl, both aged just 15, have been arrested after a 29-year-old woman was allegedly attacked with a machete at a petrol station in Melbourne.

The boy faces multiple charges over the alleged attempted carjacking of Crysta Healey in Dandenong on Sunday night.

She had put petrol in her car at 6.35pm and had gone to pay when a group allegedly approached her.

The group demanded her keys and when she refused, allegedly hit her in the arm with the machete.

Detective Acting Sergeant Sam Douglas from Victoria Police described what happened as “low, dirty and cowardly”.

A 15-year-old boy from Baw Baw and a 15-year-old girl from the La Trobe region have both been arrested.

The boy was charged with attempted aggravated carjacking, intentionally causing injury, theft of a motor vehicle and weapon offences.

He is set to appear before a bail justice, where police will ask for him to be remanded in custody.

The teenage girl was interviewed and released.

Detectives continue to investigate.