The budget carrier will also halt more than 80 per cent of services by midnight tonight as an interim measure.
Only some UK-Ireland flights are expected to continue.
The move is the most dramatic yet as airlines significantly cut flights because of travel restrictions and a drop in demand of up to 80 per cent following the Covid-19 outbreak.
It said: “Over the past few days, the spread of the Covid-19 virus has led most EU governments to impose severe travel bans and restrictions, which have had a negative impact on the schedules of all Ryanair airlines, causing widespread cancellations and travel disruptions across the network.
“We advise customers considering travel that all government travel restrictions must be followed.
“The situation changes on a daily basis, and we encourage customers to check relevant local guidelines issued by their government before they travel, and our travel advisory page for more information on country-specific restrictions.
“Our flight schedules have been hugely disrupted by these government restrictions and will be subject to further cuts.
“From midnight on Wednesday 18 March until midnight on Tuesday 24 March, Ryanair Group airlines will cut flight schedules by over 80 per cent.
“All affected customers will receive an email to advise them of their options.
“We kindly ask customers not to call us as our call centres are overloaded dealing with customer queries.
“From midnight on Tuesday 24 March we expect most if not all Ryanair Group flights will be grounded, except for a very small number of flights to maintain essential connectivity, mostly between the UK and Ireland.”
“Ryanair sincerely regrets all disruptions caused by this unprecedented Covid-19 crisis.
“All our thoughts and prayers are with our people and our customers and their families as we work our way through this crisis.”
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