THE sound of breaking glass was followed closely by a fireball explosion as petrol bombs landed around the officers' feet.

Rioters followed up the first wave of Molotov cocktails with a hail of stones and bricks that bounced off the reinforced plastic shields.

Police officers' eyes darted nervously at members of the gang before making a tactical retreat to regroup.

Then they moved forward at speed to disperse the group of demonstrators who had brought chaos to the streets.

After the trouble had subsided, the strong smell of burning remained.

The incident, at Durham Police's training facility in Meadowfield, was only an exercise - but officers are training for the real thing.

Yesterday marked the official opening of the £2.5m facility in Edwardson Road.

It is thought to be the biggest and the best-equipped public order centre outside the Metropolitan Police area.

Chief Inspector Helen McMillan said: "It is fantastic and really realistic.

"Any possible scenario, from a violent individual in a house to a large-scale disorder on the streets, can be played out and the officers are trained to deal with that."

Each year, about 200 officers from Durham Constabulary undergo extensive public order training at the complex.

Officers from Cumbria and Cleveland are also trained at the former industrial site, which was converted for police use in the summer of 2005.

The formal opening was delayed while huge improvements were made to the location and its facilities.

In the past two years, office accommodation, shower and changing rooms, a canteen, a reception area, gymnasium and classrooms have been built.

Members of Durham Police Authority were yesterday given a guided tour of the site to see the range of incidents officers are equipped to deal with.

Instructors also gave demonstrations in officer safety and first aid.