A police officer has been assaulted at a shopping centre in Melbourne's west after he attempted to arrest a teenager accused of shoplifting during the Boxing Day sales, police said.

Paramedics were called to Highpoint Shopping Centre just before 5pm following reports a man his 20s had suffered upper body injuries, an Ambulance Victoria spokeswoman confirmed.

The officer was in the process of handcuffing a teenage boy following an alleged shoplifting incident at the Rosamond Road centre when a second teenager stepped in and assaulted the officer, Victoria Police spokeswoman Natalie Butler said.

She said a large group of teenagers surrounded the officer during the arrest.