Boston Mayor Martin J. Walsh announced Friday morning that the Boston Marathon will be postponed until Sept. 14 to help stem the outbreak of the novel coronavirus.

“Our expectation and hope right now is that this day will get us to a safer date," Walsh said at a news conference. “We want to make sure that we keep people safe. … That’s what all this is about."

Walsh said moving the marathon — originally scheduled for April 20 — is “a very big undertaking” and that the proposed new date of the race “jumped around like a pinball” as officials discussed it. Questions about temperature and whether the race would conflict with activities at local schools had to be considered. Canceling the race was never considered, Walsh said. Neither was running it on the original date, running it without spectators or limiting it to elite runners.

Held annually on Patriots’ Day, a Massachusetts state holiday, the Boston Marathon — which winds its way through eight Boston-area communities over the 26.2 miles — attracts a field of more than 30,000 runners and crowds that annually exceed 500,000 along the route, generating more than $200 million for the area’s economy. Massachusetts Gov. Charlie Baker said he will push state legislators to make Sept. 14 a state holiday called Marathon Day this year and that they have shown a willingness to do so.

Walsh also discouraged anyone from running the race route on its original scheduled date, saying the roads will not be closed.

The Boston Marathon, which began in 1897, had been altered only once: in 1918 during World War I, when a military relay race was held instead.

Other marathons across the globe have been affected by the coronavirus, with Rome canceling its competition and Paris moving its race to October. On Friday, officials delayed the London Marathon until Oct. 4. It had been scheduled for April 26.