LONDON (Reuters) - Five men were crushed to death when a concrete wall collapsed at a metal recycling site in Birmingham, Britain's second-largest city, the local West Midlands Police force said on Thursday.

Emergency services were trying to recover the bodies of the five men from the site and a sixth man was in hospital being treated for leg injuries that were serious but not life-threatening, Detective Superintendent Mark Payne told reporters.

The wall that collapsed was estimated to be between roughly 3.5 meters to 4.5 meters high, Payne said.

The West Midlands Fire Service described the scene as extremely challenging, saying it involved "significant tonnage of concrete and metal and a structure that is still unstable".

The accident took place in the morning at a busy site called Hawkeswood Metal in the Nechells area of Birmingham.

"At the minute we are simply trying to recover the bodies of the men and we're doing it in a way that will help us in the future to understand exactly how that wall came to fall down," Payne told reporters in a televised briefing at the scene.

He said there were records of people entering and leaving the site and emergency services were confident they had accounted for all those present at the time of the accident.

"I've seen the scene and there is nobody alive in that scene," he said.

There was no evidence of any explosion at the site, or that fire damage could have caused the collapse, Payne said, adding that the investigation into the causes of the accident was likely to take several weeks.

He said specialist officers were supporting the families of the five victims.

(Reporting by Estelle Shirbon; editing by Stephen Addison and Kate Holton)