Additional reporting by Digital Desk staff
New car registrations were down by 63% in March compared to the same month last year.
Just over 6,000 were registered last month, compared to over 16,000 in March 2019.
While the figures for the year to date are down just over 20%.
Brian Cooke, SIMI Director General, commenting on the market figures said the motor industry is feeling the "devastating impact" of the Covid-19 pandemic.
He said: "Even before the crisis commenced, the new car market was in decline, and this fall has accelerated rapidly in the last fortnight with new car activity down nearly two-thirds on last year.
"Whatever the duration of this crisis, once we emerge, we will need to see decisive and ambitious action from Government to protect the nearly 50,000 jobs in our sector.”
Used car imports for March have also seen a sharp decline - they have almost halved compared to the same time last year.
They are down by a third for the first three months of this year.
Mr Cooke added that the motor industry will assist in "any way we can during this pandemic."
“The health of our nation is the overriding priority," he said.
"While showrooms, service and other activities within the Industry are closed, members are available to assist in emergency call-out or delivery services.
"This will be vital in keeping essential and emergency services moving."