Racing's first four Classics of the season - including the Derby at Epsom - have been postponed because of the coronavirus pandemic.
Next month's Guineas meeting at Newmarket, featuring the 1,000 and 2,000 Guineas, is off.
The Derby meeting in June, which includes the Oaks, is also affected, said Jockey Club Racecourses.
Meanwhile, organisers of June's Royal Ascot say the meeting will not "take place as an event open to the public".
"It may prove possible to run the Royal Ascot races behind closed doors, dependent on government and public health policy and the approval of the BHA [British Horseracing Authority] for us to re-start racing," said Ascot Racecourse's chief executive Guy Henderson.
Customers who have bought tickets and/or hospitality for the meeting will be refunded in full.
"We thank everyone in advance for their patience and understanding in completing this substantial task given the challenging practical circumstances of the current national lockdown," added Henderson.
The total attendance over five days at last year's Royal Ascot meeting was more than 290,000.
Talks are under way over rescheduling the big Classic races - which are solely for three-year-old horses - later in 2020.
Jockey Club Racecourses said the Guineas fixture (2-3 May) and the Derby meeting (5-6 June) were being called off "due to the ongoing public health emergency".
"As a sport we have a responsibility to safeguard the staging of our Classics, and to position them within a sensible, balanced schedule of complementary events wherever possible," said Ruth Quinn, director of international racing and racing development at the British Horseracing Authority.
"We will continue to work together to deliver the optimal outcome within these unprecedented set of circumstances.
"We are developing plans to help ensure that a suitable race programme, for the long-term health of the sport, can be delivered in these challenging times. Naturally one of the key priorities is the staging of the generation-defining races.
"The plan will adapt depending on when racing recommences, but will aim to ensure that we provide suitable opportunities for the horses most likely to define the future of the thoroughbred breed if at all possible."
Pinatubo, owned by Sheikh Mohammed's Godolphin team and trained in Newmarket by Charlie Appleby, had been favourite for the 2,000 Guineas and the Derby.
In January, the colt was given an official rating above the legendary Frankel at the same age and the highest for a juvenile racehorse in Europe for 25 years.
There are five Classics in the British Flat racing season, concluding with the St Leger at Doncaster in September.
It was announced on 17 March that all British racing would be suspended until at least the end of April.
BBC horse racing correspondent Cornelius Lysaght
Though, like all sports, flat racing is currently suspended, it believes its significance to the economy and its generally large, unenclosed arenas - making individual distancing easier - means it should be one of the first to resume.
It's with that in mind that Ascot officials talk about doing it all behind closed doors, though it's hard to imagine how a Royal Ascot without crowds and maybe without the Queen would feel - while racing and thoroughbred breeding rely so heavily on the Classics for their structures that organisers are almost obliged to plan to reschedule them.