With 10 days to go before the Olympic Games open in London, questions over the provision of security guards for the event are dominating the British media.

Thousands of team officials and athletes are arriving this week, and throngs of visitors are expected to follow. But should they be worried?

The security concerns were triggered last week when it emerged that private security contractor G4S, which was supposed to have provided 10,400 guards for the Olympics and Paralympics, would not be able to deliver.

Its failure to recruit, train and vet enough staff in time led the government to announce last week that it was deploying an extra 3,500 troops to cover the shortfall.

G4S said it has only about 4,000 guards trained and ready, although it hopes to have 7,000 fully accredited by the time the Games begin on July 27.

While the recruitment failure by G4S is highly embarrassing for the company -- and led its share price to drop sharply -- the Games' organizers insist that their contingency planning will keep everyone safe.

Visitors can certainly expect to see far more visible security measures in place than usual at Games venues and transport hubs.

Sebastian Coe, the chairman of the London organizing group, LOCOG, said Tuesday that the only real difference resulting from the G4S debacle would be in who is performing the security checks.

"The numbers really haven't changed. It's really simply about the mix of security on the park," he was quoted as saying by the Press Association news agency.

LOCOG is working with G4S to try to ensure that as many people as possible are accredited in time, Coe said, adding, "This is not a failure in numbers. We've got the numbers there. There's no compromise on security."

Home Secretary Theresa May gave a similar message last week as she was grilled by lawmakers on the matter, saying, "There is no question of Olympic security being compromised."

Critics have been less positive, with some Labour Party lawmakers concerned that security will be inadequate or that visitors will be made uncomfortable by a prominent military presence.

The chief executive of G4S, Nick Buckles, was forced to agree Tuesday under questioning from lawmakers that the security staffing fiasco is "a humiliating shambles for the country."

The Home Office said Monday that G4S is suffering from a software problem, which means the contractor cannot guarantee who will turn up where and whether guards have the right training.

The guards employed by G4S will be responsible chiefly for such tasks as providing venue perimeter security, a spokesman for the contractor said. This includes manning X-ray machines, searching people, searching vehicles and operating closed-circuit television systems, he said.

People with tickets for Olympic events have been sent e-mails giving details of the security requirements for each venue. These include airport-style limits on the size of bags that can be carried and the quantity of liquids that can be taken in.

One such e-mail reads, "Be prepared for security checks when you arrive: this will be like taking an international flight at an airport. It will be busy and you will have to queue, so get there early."

The 17,000 British military personnel deployed for the Games, including the extra 3,500 troops called up at short notice, are to help out with the security checks and stewarding at venues, as well as specialist tasks such as bomb disposal and sniffer dog searches.

Military jets and helicopters are also on standby around the capital, ready to respond to any threat, and new airspace restrictions came into force Saturday around London and the southeast.

The Royal Navy's largest ship, the helicopter carrier HMS Ocean, is now moored in the Thames off Greenwich, where it will act as a base for helicopter operations and house 400 troops providing security at the Greenwich Park Olympic venue.

Police in London and elsewhere also will play a big role in ensuring security.

Well before the G4S debacle hit the headlines, London's Metropolitan Police Service, known as the Met, was planning what it says is its biggest-ever peacetime operation.

The operation will "run for 66 days and cover over 1,000 venues, including those hosting Olympic and Paralympic sports, cultural events and 2012-themed celebrations taking place across the capital," the website says.

On the busiest days, up to 9,500 police officers will be used, including some from forces outside London, for Games-related operations, it says. Officers at Olympic venues will focus on preventing crime and keeping people and their property safe, while G4S is responsible for the security operation, it says.

Away from the venues, the Met will also have to provide the usual policing for the city and its visitors.