POLICE are investigating whether intruders instigated three attacks at two Sydney high schools - one of which featured on YouTube with a rap soundtrack.

Three attacks on students in that time have involved intruders onto the school grounds, with footage of one violent brawl attracting a global audience.

In each case race may have played a factor in the violence.

In the largest fight, a confrontation between two groups at Cumberland High School escalated out of control about 1pm last Thursday after about 10 intruders sparked a fight. The brawl lasted no more than a few minutes, but led to three students being injured and an 18-year-old former student facing charges.

As reported in the Herald on Saturday, the school was put into immediate lockdown after the lunchtime attack and police were called.

By the start of this week, videos of the fight were running on the YouTube website.

The YouTube videos - most of which have been removed - show fist fights between two groups of males at the school.

One clip is tagged "Cumberland High Fight - Wogz vs Azns", while another is titled "Cumberland High School fight with Taliban part2". Another video, titled "Chicken", shows a student being repeatedly kicked by about eight others as he lies on the ground.

-All versions of this video have been removed from YouTube in their latest bout with censorship.