impassable

Mr Guist said stones and gravel had washed down from the Mourne Mountains making some roads in the area almost impassable for vehicles.

What land routes exist in the province are nearly all dirt roads and the wet climate means they are often impassable.

Local officials had warned it could be impassable for days.

By the time the men were found in the early hours of Friday, rising water levels meant the simplest way out was impassable, forcing the rescuers and the cavers to retrace their steps.

The authorities there have ordered a mandatory evacuation of Hatteras Island, warning that the main highway linking Hatteras to other islands could become impassable.