Police, fire and ambulance crews participate in a drill in the event of a bomb attack during the Olympic games, at a disused underground station in London February 22, 2012. Dazed travellers emerged from a London underground station on Wednesday, some coughing, some covered in blood, and some on stretchers as dozens of police and emergency workers swarmed outside as part of a massive pre-Olympic drill.   REUTERS/Luke MacGregor
Police, fire and ambulance crews participate in a drill in the event of a bomb attack during the Olympic games, at a disused underground station in London February 22, 2012. Dazed travellers emerged from a London underground station on Wednesday, some coughing, some covered in blood, and some on stretchers as dozens of police and emergency workers swarmed outside as part of a massive pre-Olympic drill. REUTERS/Luke MacGregor
Police, fire and ambulance crews participate in a drill in the event of a bomb attack during the Olympic games, at a disused underground station in London February 22, 2012. Dazed travellers emerged from a London underground station on Wednesday, some coughing, some covered in blood, and some on stretchers as dozens of police and emergency workers swarmed outside as part of a massive pre-Olympic drill.   REUTERS/Luke MacGregor
Police, fire and ambulance crews participate in a drill in the event of a bomb attack during the Olympic games, at a disused underground station in London February 22, 2012. Dazed travellers emerged from a London underground station on Wednesday, some coughing, some covered in blood, and some on stretchers as dozens of police and emergency workers swarmed outside as part of a massive pre-Olympic drill. REUTERS/Luke MacGregor

London - London's emergency services started a major two-day training exercise Wednesday simulating a terror attack on the Underground during the 2012 Olympic Games.

Emergency services poured into the disused Aldwych subway station to test their responses to another major attack like the 2005 London bombings.

Some 2,500 people, ranging from ordinary fire, police and ambulance crews up to police chiefs and the government's COBR emergency response committee are being put to the test.

Home Secretary Theresa May and other senior ministers are taking part in the exercise.

“We are taking no chances and thoroughly testing of all our systems across government, Games organisers and the emergency services so that we are prepared for anything and everything,” said London Mayor Boris Johnson.

The London bombings of July 7, 2005 took place the day after the British capital won the right to host the 2012 Games.

Four home-grown Islamist suicide bombers struck in a coordinated attack on three underground trains and a bus, killing 52 people and wounding more than 700.

The MI5 domestic security service says the threat level from international terrorism is substantial - the middle of five levels - meaning that an attack is considered a strong possibility. - Sapa-AFP