Celtic have promised to investigate an overcrowding incident at Sunday's Old Firm derby match that led to five people being injured.

Hundreds of supporters became stuck outside the North Stand ahead of the meeting with Rangers, which the champions won 1-0.

According to Chief Superintendent Brian McInulty of Police Scotland, five people were hurt, one of whom was taken to hospital after falling from a wall, in what some fans described as "a crush" outside the ground.

"People couldn't walk round the stadium anymore, so there was a bottleneck under the north stand," an unnamed fan told BBC Sport.

"Suddenly there was an absolute crush because there were about 1,000 people trying to get one way and about 1,000 trying to go the other way. The corridor is only six to seven people wide.

"They kept letting people through from either side of the corridor and it became a crush, with people getting semi-trampled.

"I was behind a woman with a boy of about 10 who was getting rocked and people were panicking and climbing over the fences as they couldn't actually breathe properly. It was that bad."

Another supporter, named as Martin Lennon, told Sky Sports: "The scenes were shambolic. After being refused access down London Road, I tried to go through the Janefield Street tunnel, the main route round the stadium.

"When I got there I found myself among thousands of supporters who were blocked from using the tunnel. There was no warning, no explanation, nothing over the PA system, no details about alternative routes and only a handful of police."

Celtic later issued a statement in which they vowed to work with police to find out what happened.

"We are aware of the issues caused by congestion prior to kick-off," they said. "We are pleased that stewards and police were able to assist quickly and we thank our supporters for their patience shown while the matter was being dealt with.

"We will work closely with police to investigate and review this matter. The safety of our supporters will always be our priority."