Anti-terror police are to swoop on a shopping centre in a training exercise to test their response to a Paris or Brussels-type attack on civilians.

Armed with machine guns, officers from the North West Counter Terrorism Unit will drill their training techniques and counter-terror tactics during the exercise at the huge intu Trafford Centre shopping complex, starting at midnight on Tuesday.

About 800 people will be involved in the role-play exercise, including volunteers and fire and ambulance service personnel, with police wanting to make the "attack" as realistic as possible.

The exercise will stretch over three days, involving a second location on Merseyside.

Exact details have not been made public and are known only to a few senior officers, who will direct different scenarios such as possible hostage taking, mass casualties or suicide bombers, to test how the emergency services respond to "fluid" and developing situations.

Police stress there is no specific threat to the shopping centre and the exercise has been planned since last December, but it will give them and businesses the opportunity to test their emergency terror response.

The current UK terror threat level is described as severe, meaning an attack is highly likely, according to the security services.

The exercise, codenamed Exercise Winchester Accord, is the fourth major exercise in months, coming after previous ones in London, Glasgow and Essex.

The latest drill takes place while the shopping centre is closed to the public between midnight and 6am.

Over the following two days it will continue in locations in the North West, including Red Bank Community Home, a disused young offenders' centre in Newton-le-Willows, Merseyside.

Assistant Chief Constable Rebekah Sutcliffe of Greater Manchester Police (GMP) said: "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.

"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.

"This exercise is part of a national programme that has been planned extensively for five months.

"We have worked closely with intu Trafford Centre and other emergency services to test our response to a major terrorist incident in a public place, which for part of this exercise is a shopping centre.

"Residents in the area may hear loud noises and see emergency services activity around intu Trafford Centre during the exercise and I can reassure people that there is no cause for concern.

"However, I would still urge people to contact police if they do have any concerns or want to report anything and are not sure if it is linked to the exercise.

"This exercise has allowed us to build and strengthen our relationship with intuTrafford Centre and I would like to thank them for allowing all the participants to use their centre. Their support in the planning of this exercise demonstrates their commitment to test their response to a major incident and protect their staff and customers."

Richard Paxton, general manager of intu Trafford Centre said: "The police and emergency services do an extremely important job keeping the public safe. This training, planning and preparation to deal with all eventualities is essential and we had no hesitation allowing them to use our facilities for their exercise while the centre was closed."

Any suspicious activity or behaviour can be reported to police via the confidential Anti-Terrorist Hotline by calling 0800 789 321. Extremist or terrorist content online can be reported at www.gov.uk/report-terrorism.