Elderly man attacked by teenagers at Castle Hill bus stop

An argument between an elderly man and a group of teenagers in Sydney's north-west has ended with a violent attack caught on film.

NSW Police told 9NEWS they are investigating the incident involving the 70-year-old at a bus stop on Old Castle Hill Road last Saturday.

In the footage, which was posted to Instagram, a young male is seen arguing with the older man outside Castle Towers shopping centre.

The younger man backs away before falling backwards over the edge of a footpath.

This prompts another young male in a red beanie to push the older man into the illuminated bus stop.

Curled up on the ground, the two youths, aged 16, kick the man repeatedly in the stomach while a young female in the background yells at them to stop.

Police said they arrested one of the teenage boys at the scene, and have identified the other young person involved.