The first wave of athletes and visitors began pouring into Britain yesterday and officials played down fears that a packed London would buckle under the pressure of its biggest peacetime security and transport operation.

Heathrow said athletes from 50 nations will touch down in what is being described as Britain's biggest peacetime transport challenge. In all, the airport will handle some 236,955 passengers, breaking the previous daily record of 233,562 set in July 2011.

To cope with the deluge, Heathrow has enlisted some 1,000 volunteers to greet arrivals - 500 were working yesterday itself - and created special teams to deal with oversize items like Olympic javelins, bikes and other sports equipment. All wore bright pink to easily stand out.

The London Olympics start July 27 and end August 12.

An embarrassing shortage of security guards, fears over airport queues and questions about the capital's creaking transport system have overshadowed preparations for the Games.

Extra soldiers were drafted in to help police the Games after private security firm G4S said it had run out of time to train all its newly recruited staff.

Less than two weeks before the opening ceremony on July 27, Prime Minister David Cameron said the G4S shambles would not compromise Britain's largest policing exercise.

"We had contingency plans, we are using those contingency plans and we will do whatever it takes to deliver a safe and secure Games," Cameron said.

Some 12,500 police will be on Olympics duty each day, backed up by soldiers, fighter jets and missile batteries on the top of apartment blocks near the Olympics site in east London.

The International Olympic Committee said safety levels have not been compromised.

"Of course security is paramount and important for everyone. I think there has been a good show of flexibility with the problem that arose," IOC President Jacques Rogge said.