LONDON (AP) ― London should not be turned into a “city under siege” by the heavy security measures being put in place for the Olympics, London organizing chief Sebastian Coe said 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 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-Aug. 12 games.

Typhoon fighter jets from around Britain arrived 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 World War II. The Royal Air Force is also sending Puma transport helicopters and Lynx helicopters carrying teams of snipers trained to intercept aircraft flying without authorization 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.

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.