Police have simulated a terror attack at one of the UK’s largest shopping centres as part of a counter-terror exercise.

A mock suicide bomber acted out an explosion at Manchester’s Trafford Centre overnight as hundreds of people ran screaming and hid in shops and restaurants.

Around 800 people were involved in the exercise, which started at midnight, when a man dressed in black walked in and shouted at the crowd.

Emergency services and volunteers take part in a simulated terror attack at the Trafford Centre in Manchester on 10 May 2016. (Getty Images)

Moments later an explosion rocked the food hall and volunteers, wearing ear defenders and safety glasses, dropped to the floor.

Many wore make-up to simulate serious injuries and others screamed out for help in The Orient food court as the sound of gunfire rang out.

Armed officers then moved in, practicing tactics drawn up in the event of a Paris or Brussels-style attack.

Police stressed that there was no specific threat to the Trafford Centre, which is the second-largest in the UK.

In pictures: Terror attack exercise in Manchester Show all 7 1 /7 In pictures: Terror attack exercise in Manchester In pictures: Terror attack exercise in Manchester Counter-terror exercise at the Trafford Centre The emergency services and volunteers take part in a simulated terror attack at the Trafford Centre on 10 May, 2016 in Manchester, England. PA In pictures: Terror attack exercise in Manchester Counter-terror exercise at the Trafford Centre Emergency forces and shoppers take part in a simulated terror attack at the Trafford Centre on 10 May, 2016 in Manchester, England. Getty Images In pictures: Terror attack exercise in Manchester Counter-terror exercise at the Trafford Centre The emergency services and volunteers take part in a simulated terror attack at the Trafford Centre on 10 May, 2016 in Manchester, England. Getty Images In pictures: Terror attack exercise in Manchester Counter-terror exercise at the Trafford Centre The emergency services and volunteers take part in a simulated terror attack at the Trafford Centre on 10 May, 2016 in Manchester, England. Getty Images In pictures: Terror attack exercise in Manchester Counter-terror exercise at the Trafford Centre Emergency services and volunteers take part in a simulated terror attack at the Trafford Centre in Manchester on 10 May 2016. Getty Images In pictures: Terror attack exercise in Manchester Counter-terror exercise at the Trafford Centre Emergency services and volunteers take part in a simulated terror attack at the Trafford Centre in Manchester on 10 May 2016. Getty Images In pictures: Terror attack exercise in Manchester Counter-terror exercise at the Trafford Centre People playing the role of injured shoppers react during an exercise at the Intu Trafford Centre in Trafford, Manchester, on May 10, 2016. PA

Greater Manchester Police, the North West Counter Terrorism Unit and the North West Ambulance Service were all being tested, with no personnel being told precisely how the “attack” would unfold.

The Manchester Evening News reported that the SAS was also involved in the operation, which took place while the shopping centre was closed between midnight and 6am.

Greater Manchester Police had urged the public not to be alarmed by loud noises, while the Trafford Centre’s managers praised the emergency services' “great work”.

Assistant Chief Constable Rebekah Sutcliffe said agencies were testing their response to a “major terrorist incident in a public place”.

“Our priority is to stop terrorists from planning and orchestrating attacks and with exercises like this, we can put our response to the test in a safe environment, so we are fully prepared for a time when it may be critical,” she added.

The emergency services and volunteers take part in a simulated terror attack at the Trafford Centre on 10 May, 2016 in Manchester, England. (Getty Images)

“I want to make it clear that this is not linked to any specific terror threat or attack, but is an opportunity for us to make sure we are in the best position possible, should a terrorist attack happen in the North West.”

The drill was set to continue through Tuesday and Wednesday in locations in the region, including Red Bank Community Home, a disused young offenders' centre in Newton-le-Willows, Merseyside.

The exercise, codenamed Exercise Winchester Accord, was planned in December and is part of a national programme, coming after previous drills in London, Glasgow and Essex.