Retailers hoping for an Olympics boost appear to have suffered an early drop in business as visitors stay away from central London due to fears of overcrowding.
London's West End is hoping for more than 25 million visits over the summer, with around 90% of those arriving for the Olympics expected to shop and eat in the area.
But around 10% fewer people visited the West End and 7% fewer visited the East End last Friday and Saturday compared with the same weekend last year, according to Experian Footfall.
Tom Jenkins, chief executive of the European Tour Operators Association, said: "This is entirely predictable.
"London has approximately 300,000 foreign and 800,000 domestic visitors every day in August. These people have been told implicitly that they should stay away and they have done so.
"The numbers are currently dramatically down on last year. How far down will be determined by how long Transport for London maintains the 'don't come into London' campaign.
"But they have been replaced by approximately 500,000 Games ticket holders, many of whom are Londoners, all of whom are here because they've come to watch sport. They are not necessarily interested in London as a tourist destination. They are not here to shop, sightsee or dine out.
"This has occurred in every other Olympics games."
He added: "While it's bad news for the service industry, it's great news for those here and those thinking of coming here. I imagine that if you visited the Tower of London you'd have your own personal Beefeater to show you around."
Experian noted that footfall in the East End recovered on Sunday to an increase of 12% on last year, with a spokeswoman saying: "Shopper attention may have been diverted on Friday and Saturday by the lure of the opening ceremony and the first events but by Sunday we see an uplift in footfall in London's East and West End, suggesting that over the next few weeks the Games will provide many opportunities for retailers to capitalise on."
The New West End Company, which represents leading retailers in Bond Street, Oxford Street and Regent Street, said stores were hoping for a boost in spending with more than three times the amount of Olympic sponsors and officials taking part in the Games than in the previous Olympics.
Jace Tyrrell, director of communications at the New West End Company, said there had been an expected drop in tourists.
"There's been displacement towards the Olympics and fewer tourists as expected, but there's also been a boost from the Olympic family, who spend more, and numbers of Olympic family are higher than we've had before."
British Retail Consortium spokesman Richard Dodd said the downturn in numbers was not the whole picture.
He said: "The overall picture is that the boost that we are expecting from the Olympics is partly about overseas visitors shopping in London whilst they are here. It would certainly be disappointing if there were a reduction in domestic shoppers at the expense of this.
"But another really big part of the Olympics is a boost in food and drink sales, and this is likely to be bigger and last longer than the jubilee.
"Some people's impression that the West End is quieter than it usually would be is not the whole picture."
The drop in business since the start of the Olympics also appeared to be affecting some of London's most-visited tourist attractions.
Employees at both the Imperial War Museum and the London Dungeon said there seemed to be fewer visitors than normal, with one describing things simply as "dead".
Paul Wild, 53, a member of staff at the Imperial War Museum in Southwark, south London, said: "We were expecting a lot more people but so far it has been really quiet and our normal visitors don't seem to be coming.
"I don't know if it has to do with everybody being warned not to come to London, that was stressed so much.
"We usually have lots of families with kids at this time of year because the children are off school, but so far it has been quieter than we expected."
The situation appeared to be similar at the London Dungeon, an attraction which recreates macabre historical events and usually boasts long queues at its entry next to London Bridge railway and Underground station.
James Russell, a 25-year-old member of the attraction's promotion staff handing out leaflets on the street dressed in costume, said things had been "slower" since the start of the Games.
He said: "A lot of people seem to be heading over to the Olympic Park rather than coming in, but it is still too early to say if it will affect us after the first week.
"I'm pretty sure it will pick up when visitors are done with seeing events at the Games, they will want to see other things and this is one of the best attractions in London."