A building has "collapsed" into a busy London underground station as part of the biggest disaster training exercise ever seen in Europe.

Exercise Unified Response , coordinated by the London Fire Brigade, simulated a tower block collapsing into Waterloo station to prepare specialist emergency crews for a large-scale operation with mass casualties.

An actor has make-up applied for the Unified Response training exercise at Littlebrook Power Station Photo: PA

The four-day exercise, which started on Monday, is designed to test the contingency planning of more than 70 organisations, from mortuaries to the Government’s Cobra committee, local councils and search and rescue teams.

"When disaster strikes families need to be confident that the authorities are doing everything they can to identify their loved ones in a dignified and respectful way."

"When disaster strikes families need to be confident that the authorities are doing everything they can to identify their loved ones in a dignified and respectful way." Chief Constable Debbie Simpson

It is being staged at a disused power station near the Dartford Crossing as well as at four separate venues in central and south east London.

The drill, which is costing £770,000 and is funded by the European Union, involves eight real tube carriages, tons of rubble and more than 2,000 volunteers playing casualties, bystanders and worried relatives.

One carriage is buried so deep in the rubble that emergency crews will not immediately see it.

The request for assistance to the Emergency Response Coordination Centre will be made through the UK's official channels, including the Cabinet Office.

As workers first arrive on the scene, they will be confronted with tube ticket barriers smeared with blood. Casualties, whose injuries have been realistically created by local make up artists, will be suffering from a range of head injuries, lacerations, glass wounds, broken legs and amputations.

Disaster victim identification (DVI) teams from all UK police regions are working alongside other forensic specialists.

More than 250 personnel are working at the scene and in a specially constructed temporary mortuary.

The emergency services training exercise is taking place at Littlebrook Power Station in Dartford Photo: PA

It is the biggest multi-agency training exercise in London Fire Brigade's history.

Ron Dobson, London Fire Brigade’s commissioner, has described tube tunnels as “the worst place possible” for rescues, with moving trains and live wires adding to the danger.

He told the Evening Standard: “We needed to create a realistic scenario, there’s hundreds of thousands of tons of rubble.

Great work by the make up teams for #UnifiedResponse pic.twitter.com/plbogyNxJq — John Pannell (@johnpannell) February 29, 2016

“The idea is there’s been the collapse of a high-rise building above Waterloo station that’s gone down into the station itself (and) caused some collapse in the tunnels, there are some Underground trains caught up in it and people trapped.

"There’s lot of other hazards down there we need to be careful of. In something like 7/7 you have to take them from the tube train, along the lines and out the platforms.

In recent years, specially trained teams from around the UK have been deployed to assist in the downing of Malaysia Airlines Flight MH17 in July 2014 and the Shoreham air crash in August last year.

One carriage is buried so deep in the rubble that emergency crews will not immediately see it Photo: PA

“One of the things we were criticised for on 7/7 was confusion between emergency services. It took us too long to agree there wasn’t a chemical involved. That wouldn’t happen in future.”

Chief Constable Debbie Simpson, of the National Police Chiefs, said: "Victim identification is never a pleasant subject to discuss but it is unfortunately a reality. When disaster strikes families need to be confident that the authorities are doing everything they can to identify their loved ones in a dignified and respectful way, whilst supporting any criminal investigation.

• Behind the scenes on a disaster-training simulation

"Importantly this process cannot be hurried. As frustrating as this can sometimes be, especially in a world of fast paced mainstream and social media, we have to be meticulous in our approach to ensure we achieve reliable scientific identification.

More than 250 personnel are working at the scene Photo: PA

"It's not often we get to test working practices on such a scale and it's really positive to see so many of our European colleagues involved. Effective evaluation and debriefing will help highlight good practice and any areas for development."