BOSTON (AP) — The Latest on the 121st running of the Boston Marathon (all times local):

9:20 a.m.

The 121st running of the Boston Marathon is getting underway in waves for the 30,000 athletes.

Mobility impaired athletes — the blind and those with prostheses or other challenges — started at 8:50 a.m. Monday.

They were followed by the men’s push rim wheelchair athletes at 9:17 a.m., and the women two minutes later.

The elite women start at 9:32 a.m., and the elite men and the rest of wave one get underway at 10 a.m.

There are three more waves that set up a staggered start: wave two at 10:25 a.m., wave three at 10:50 a.m. and wave four at 11:15 a.m.

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8:50 a.m.

The 121st running of the Boston Marathon is officially underway with the mobility impaired athletes.

Runners who are blind, wear prostheses or have other challenges set off from Hopkinton, Massachusetts, on Monday morning.

The rest of the field will follow in waves.

Monday’s race is getting started in temperatures of 66 degrees Fahrenheit (19 degrees Celsius.) That’s ideal for spectators but a bit warm for many runners.

The leading men will include Galen Rupp, the bronze medalist in the Rio Olympics, running Boston for the first time, and 2014 champion Meb Keflezighi (kuh-FLEHZ-key.)

The top U.S. woman is Desi Linden, a two-time Olympian who’s placed in the top 10 in Boston three times.

Security has been extra tight since 2013, when bombs killed three spectators and wounded more than 260 others.