AP Photo/Lefteris Pitarakis
Security personnel use sniffer dogs to check vehicles at the Mall in central
The London marathon takes place on Sunday, less than one week after Monday's fatal explosions at the Boston marathon, which killed three people and injured close to 200.
British authorities have beefed up security in the wake of the tragedy, deploying hundreds more officers than previous races, The New York Times' Alan Cowell reports.
Chief Superintendent Julia Pendry said: "It is a good 40 percent increase on last year on numbers of officers on the ground. We’ve got more search dogs out; we have got more on high-visibility patrols."
More than 36,000 runners are expected to take part in one of the world's largest marathons.
The 26.2-mile race, which ends at The Mall, typically pulls in one million spectators and $180 million in economic activity, a spokeswoman for London's official tourism agency told NBC News' A. Pawlowski.
Runners will honor a 30-second moment of silence at the starting line for the Boston victims.
AP Photo/Lefteris Pitarakis