London: London should not be turned into a "city under siege" by the heavy security measures being put in place for the Olympics, London organising chief Sebastian Coe said on Wednesday.

Coe spoke as the British military embarked on operations to test Olympic security, including flights over London by fighter jets and helicopters. Visitors to the Olympic Park encountered lengthy delays at times on Wednesday as they went through airport-style security checks.

"We want to make sure these games are safe and secure, but at the same time we are not presenting a vision of London that is a city under siege," Coe said inside Olympic Stadium.

About 75,000 spectators are expected at Olympic Park on Saturday for five test events ahead of the July 27 to August 12 games.

Air cover

Typhoon fighter jets from around Britain arrived on Wednesday at a Royal Air Force base at Northolt in west London for the test operation, code named Exercise Olympic Guardian. It is the first time that fighter aircraft have been stationed at RAF Northolt since the second World War.

The Royal Air Force is also sending Puma transport helicopters and Lynx helicopters carrying teams of snipers trained to intercept aircraft flying without authorisation in London's airspace.

"What we will have is a plan that has many levels to it, which will allow us to deal at one end — which is that 9/11-type attack — perhaps down to the lower and the slower type of threat that we may face," said Air Vice-Marshal Stuart Atha, air component commander for Olympics air security. "There is no specific threat and all we are doing is having in place what we would describe as prudent and appropriate measures ... [so] we could react, if required, in a timely and appropriate fashion."

On the ground, British soldiers are also testing missile systems that may be based on buildings and apartment blocks near the Olympic site in east London.

Delays

Coe said some delays at Olympic Park were to be expected during the tests.

"We are testing particularly spectator flows, we are testing our security systems, but there will be some queuing — this is an Olympic Games," Coe said. "Whether it's the Olympic Park, whether it's Wimbledon, whether it's a football ground, these are not championships as usual."

But Coe said "there is no appetite for risk," and urged London natives to readjust their sports time clocks.

"If I am going to an Olympic football tournament, build in more time, plan your day around the fact that getting in and out of these venues will take longer than they will normally take, particularly if you are benchmarking it against how you get into Wimbledon, Lord's (cricket venue) or Wembley on normal games," Coe said.

Olympic visitors could also encounter delays just getting into Britain, with a growing furor over recent snaking lines and lengthy delays at Heathrow Airport's immigration desks.