The incident took place on GT Road near Sai Mandir here this morning. The unipole was in a dilapidated condition and the company installed it in an unplanned manner due to which it could not withstand strong wind and collapsed on the vehicles on road, traffic police Inspector Anil Yadav said.
Several traffic policemen were pressed into service to ease the situation and clear the movement of traffic, he said.
The injured were rushed to a nearby hospital for treatment.
District Magistrate Vimal Kumar Sharma has constituted a magisterial inquiry in the case. Sub divisional magistrate Nitin Madan will probe the matter as to whether Nagar Nigam or Ghaziabad Development Authority is responsible for awarding the contract to the "negligent" company who installed the advertising billboard on the rickety unipole.