Workers in the Perth CBD have recorded video footage of what appears to be a teenage fight club.

Alarmed witnesses called police after they saw about 20 teenagers brawling on the roof of the Queen Street carpark today.

Concerned office workers filmed the fight after seeing a young child standing just metres from the violence.

Police were told a child in a pram was present and that the fight appeared to be pre-organised.

It lasted about 20 minutes.

The group of teens continued raging on the roof and showed no signs of stopping until security guards told them police were on their way.

Officers are questioning people in the area tonight.