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.

"If I am going to an Olympic football (soccer) 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.

"I'm actually confident that by the time we get to the games these are issues that will be behind us," Coe said.

British Immigration Minister Damian Green earlier this week acknowledged problems with long waits at airport immigration lines and said Britain's border force would deploy extra staff at Heathrow.

Some of the airport waits have been blamed on heavy rains wreaking havoc on planes' arrival times.

A deluge last weekend also exposed some flaws within venues at Olympic Park. The director of venues, James Bulley, said there were a "number of leaks" but not a huge amount.

"When you put in new installations you always get teething problems," Bulley said. "We've had two or three venues where we have discovered some leaks. Those venues have been repaired. This is natural when you are going through a building process."