Portstewart promenade was hit with flash flooding late on Sunday afternoon after water surged up through the tarmac as thunderstorms brought heavy downpours.
Drivers were forced to turn around to avoid huge pools water, which have caused serious damage to the road surface on the busy seaside street.
The street was packed with large crowds just minutes earlier and many had to abandon their cars and run for cover.
Social media footage showed overflowing drains struggling to cope with the deluge of water at around tea-time.
Police officers moved in quickly to evacuate the area and close the road to further traffic.
On Sunday evening, part of the main street was left badly damaged as the road surface was ripped up.
A PSNI spokesperson said: “Portstewart Promenade is closed due to structural damage caused by adverse weather.
“Please avoid the area as there is no access to vehicles or pedestrians.
“Please be advised that the road is expected to remain closed for some time.”
Sinn Fein MLA Caoimhe Archibald has contacted the Department for Infrastructure regarding the damage.
The East Derry MLA said: “I’ve contacted the Department for Infrastructure about the damage caused to the Promenade in Portstewart due to flash floods and asked how quickly it can be repaired.
“The Promenade has been closed due to the flooding and motorists are advised to use an alternate route.
“I will also be in touch with the Infrastructure Minister about what preventative measures can be put in place to protect the promenade from future damage.”
Elsewhere, thundery downpours have caused traffic chaos on some of Northern Ireland’s major roads, including the M1 and the A4 near Dungannon as heavy rain made driving difficult.
A Yellow Weather Warning for thunderstorms was in operation over the weekend.
Monday will still see some further rain in Northern Ireland, with all that warm humid air around, but nothing on the scale of the downpours on Sunday.
Tuesday could still see some showers – especially in the west of Northern Ireland, the Met Office said.