A bomb disposal unit was called in and a high street was cordoned off after 16 white phosphorous Second World War grenades were found by builders.

The unexploded bombs were unearthed under a patio next to the function room at the former Golden Lion pub in London Colney on Wednesday.

The land is currently under construction for new flats, and a digger reportedly ran over the grenades at around 10.30am, causing a fire.

Hertfordshire Fire & Rescue were initially called to the scene in London Colney High Street, sending several crews to the scene - but the Explosive Ordnance Disposal team and police were called in it became obvious to the firefighters that this was not a routine job.

Watford Observer:

Emergency services blocked off the road to keep the public safe. Credit: Steve Kordek

Watford Observer:

The cordon was in place for a number of hours. Credit: Steve Kordek

Watford Observer:

Credit: Steve Kordek

A police cordon was put in place and a man who lives nearby said police told residents to stay indoors.

The resident said: "At first, we heard sirens and thought there was a fire.

"Four or five fire engines turned up and then the police who cordoned off the road.

"We knew it was something to do with the building site as we could see activity around one of the skips.

"Then there was a knock at the door and the police informed us to stay inside which was relatively easy to do whilst on lockdown.

"We overheard talk that there would be a detonation so we started filming and shortly later we saw the explosion.

"It was very loud and made all of the windows rattle.

"We didn't think it would be such a big blast and it took us by surprise."

At around 5pm, the grenades were placed into a skip in the pub car park and a controlled explosion was carried out.

Video footage captures the moment the bombs exploded sending a fireball into the air.

Watford Observer:

There was a fireball as the grenades were exploded in the skip. Credit: Steve Kordek

No one was injured and the cordons were lifted around an hour later.

A spokeswoman for Hertfordshire Constabulary said: "Police were called at 12.51pm on Wednesday to assist the fire service following the discovery of 16 white phosphorous World War Two grenades.

"The grenades had been found whilst a building site was being excavated in London Colney High Street.

"Officers attended the scene and put on road closures and a cordon while the Explosive Ordnance Disposal carried out a controlled explosion on site.

"The explosion was carried out at around 5pm and the roads reopened at around 6:15pm."

Watford Observer:

Credit: Steve Kordek