Mike Greenberg expresses his thoughts on the Boston Marathon being postponed until September due to the coronavirus pandemic. (1:24)

Organizers of the Boston Marathon are postponing the event until Sept. 14 because of concerns over the coronavirus pandemic, Boston Mayor Marty Walsh announced Friday.

The Boston Athletic Association, which oversees the marathon, had held off deciding the fate of the April 20 race even as other high-profile sporting events were canceled or postponed around the globe.

But pressure had mounted from officials in Boston and the seven cities and towns along the 26.2-mile course. Some had expressed worries not only for the health of the 31,000 registered runners but also the estimated 1 million spectators who traditionally line the route, giving athletes hand slaps, high-fives and even kisses as they pass.

Walsh said at a news conference that there was never a thought to limit the race to only elite runners or to restrict spectators, saying this is an inclusive event.

More than 30,000 runners registered for the Boston Marathon, which usually has 1 million spectators along the course. Mike Lawrie/Getty Images

President Donald Trump's order restricting most Europeans' travel to the United States over the coronavirus complicated efforts to salvage the race. Thousands of runners come from Europe to compete at Boston.

Walsh told potential participants not to run along the marathon course on April 20, the originally scheduled date for the race.

For most people, the coronavirus causes only mild or moderate symptoms, such as fever and cough. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia and death.

The vast majority of people recover from the virus. According to the World Health Organization, people with mild illness recover in about two weeks, while those with more severe illness may take three to six weeks to recover.

The Boston Marathon has never been canceled outright since its first running in 1897, though there was a de facto cancellation in 1918, when the end of World War I and a global influenza pandemic prompted organizers to switch to a relay race format.

Until Friday, not even the Great Depression or ferocious storms had interrupted the 124-year-old race, a destination for runners worldwide. About one-third of this year's field was from outside the U.S.

It wasn't an easy decision: Walsh said the marathon pumps $211 million per year into the city's economy -- not counting the millions more that runners raise for charities.

Massachusetts Gov. Charlie Baker had declared a state of emergency, and race organizers had said they were in close contact with the federal Centers for Disease Control and Prevention and the World Health Organization.

In recent days, the Rome Marathon was canceled, the Paris Marathon was postponed from April 5 to Oct. 18, and the Barcelona Marathon was postponed from March 15 to Oct. 25, all over concerns about COVID-19. Friday, organizers of the London Marathon announced that the race has been postponed from April 26 until Oct. 4.

This month's Tokyo Marathon was expected to have 38,000 participants but was limited to elite runners due to concerns over the outbreak of the virus. Spectators at the Los Angeles Marathon, held earlier this month, were advised to practice social distancing.

The Associated Press contributed to this article.