The Boston Marathon has been cancelled for the first time in its 124-year history.

Organizers said Thursday that they instead will have a virtual event in which participants who verify that they ran 26.2 miles (42.2 kilometres) on their own will receive their finisher's medal. The race had originally been scheduled for April 20 before being postponed for five months because of the coronavirus pandemic.

"It became clear as this crisis developed that Sept. 14 was less and less plausible," Mayor Marty Walsh said at a news conference outside City Hall, where runners traditionally gather for a prerace pasta dinner.

"This is a challenge, but meeting tough challenges is what the Boston Marathon is all about," Walsh said, invoking the response to the finish line bombings seven years ago. "It's a symbol of our city's and our commonwealth's resilience. So it's incumbent upon all of us to dig deep, like a marathon runner, like we did in 2013, and keep that spirit alive."

Although the title of Boston Marathon champion is contested by a few dozen elite athletes, the field includes more than 30,000 recreational and charity runners, with as many as one million people lined up along the course trek from Hopkinton to Boston's Back Bay.

That presented organizers with a social distancing problem that won't be solved by the fall.

"There's no way to hold this usual race format without bringing large numbers of people into close proximity," Walsh said. "While our goal and our hope was to make progress in containing the virus and recovering our economy, this kind of event would not be responsible or realistic on Sept. 14 or any time this year."

The cancellation is a first for the race, which began in 1897 when 15 men drew a starting line in the dirt in Ashland and headed for the city to commemorate the first modern Olympic Games the previous year. In 1918, the format was modified to a relay because of the First World War. The 2013 race was stopped when two bombs exploded at the finish line, several hours after the winners had finished but while many recreational runners were still on the course.

"There is a pretty rich history of accommodation and addressing reality. This is this year's reality," said Tom Grilk, the CEO of the Boston Athletic Association.

For each of those years, the race was held in April on the state holiday to commemorate the battles in Lexington and Concord that marked the start of the Revolutionary War. Traditionally, the Red Sox have scheduled their first pitch for the morning so baseball fans could wander over to Kenmore Square after the game to see the runners pass by with one mile to go.

When the race was postponed in March to Sept. 14, Mayor Marty Walsh cited the desire to salvage the estimated $211 million the event pumps into the city's economy each year. The Boston Athletic Association and marathon runners also raise about $40 million for charity.

Walsh said at the time that there was no thought of excluding the tens of thousands of amateur runners who consider running Boston a bucket list achievement. The Tokyo Marathon went on as scheduled in March with just over 200 elite runners but not the 38,000 recreational runners who had signed up. Spectators at the Los Angeles Marathon on March 11 were advised to practise social distancing.

"That's not the Boston Marathon. We're an inclusive marathon," the mayor said. "The Boston Marathon is for everyone."

The 2021 Boston Marathon is scheduled for April 19, and the 125th anniversary edition is scheduled for April 18, 2022.