Footage has emerged of a violent clash between more than 20 tradies at a construction site, prompting a police investigation.

Police are investigating a brawl involving more than 20 tradies outside a building site in Sydney’s north-west.

Police are investigating a brawl involving more than 20 tradies outside a building site in Sydney’s north-west.

A massive brawl involving more than 20 tradies erupted outside a building site in Sydney's north-west this morning.

A massive brawl involving more than 20 tradies erupted outside a building site in Sydney's north-west this morning.

A massive brawl involving more than 20 tradies erupted outside a building site in Sydney's north-west this morning.

Punches and kicks are thrown as the violence spreads down the street, with some tradies using their hard hats as weapons.

Punches and kicks are thrown as the violence spreads down the street, with some tradies using their hard hats as weapons.

Punches and kicks are thrown as the violence spreads down the street, with some tradies using their hard hats as weapons.

Punches and kicks are thrown as the violence spreads down the street, with some tradies using their hard hats as weapons.