Pakistan International Airlines (PIA) is investigating an incident when seven people were forced to stand in the aisle during a three-hour flight from Karachi to Medina.

The Boeing 777 aircraft was reportedly carrying 416 passengers on January 20 despite having a seating capacity of only 409, including jump seats. However, the incident came to light a month after the actual incident, thanks to an investigative report published by Pakistan's Dawn newspaper on Friday.

Such air safety violations can cause many problems and can put passengers' lives at risk, because the extra passengers would not have access to oxygen or could cause congestion during evacuation in case of an emergency.

The sources said that the extra boarding passes were hand-written and not computer-generated, and that the ground traffic staff was not informed about the 17 extra passengers by the aircraft crew.

Dawn reported that the cabin chief told the captain about the chaos in the cabin, but that she was told to sort out the situation as the aircraft was on the taxi way.

However, the captain said he was only informed about the situation after the aircraft closed its doors and the plane had taken off, and it was impossible for him to make an immediate landing back at Karachi.

PIA spokesman Danyal Gilani told the BBC that "the matter is under investigation and appropriate action will be taken once responsibility is fixed."