The 118th Boston Marathon, scheduled for April 21, has drawn a huge field of over 36,000 runners, which is capacity for the course and over 9,000 more than last year, Xinhua reported.
The runners include thousands who were forced to stop last year after the explosions and thousands more who want to show their solidarity with Boston.
Meanwhile, at least one million spectators, twice the usual crowd, are expected to gather along the 42 km course, many of them at the finish line on Boylston Street, where two bombs exploded, killing three people and injuring 260 others.
The security challenge is immense, in part because the event is spread across eight cities and towns along a route lined by spectators on both sides.
More than 3,500 police officers, twice last year's number, will be deployed, according to the organiser. Those plans include plainclothes officers, private security contractors, numerous security checkpoints with metal detectors, bomb-sniffing dogs and hundreds of surveillance cameras, according to BAA officials.
Spectators are being encouraged to carry their belongings in clear plastic bags to speed up security screening and nt to carry backpacks or coolers, wear vests with pockets, or bring baby strollers.
Despite the intense security upgrades, the officials said they did not want Boston to appear to be a police state.
"We are confident that the overall experience of runners and spectators will not be impacted and all will enjoy a fun, festive and family-oriented day," Kurt Schwartz, director of the Massachusetts Emergency Management Agency, said.
The marathon is held on Patriots' Day, which falls on the third Monday in April and commemorates the Battles of Lexington and Concord in 1775. It is celebrated in only a few states; in Massachusetts, it is a school holiday, which makes the marathon all the more festive.