Thousands of residents have been left without water after a large underground pipe burst.
Severn Trent Water said it had no time scale for when more than 20,000 people would see their supply fully restored, after reports of low pressure or no water at all.
The provider said the problems affecting homes to the north and east of Nottingham had been traced to a burst pipe in the village of Epperstone.
A spokesman said that a car had driven into the flooded hole caused by the high-pressure burst, which had initially "complicated" any repair. He added that it had since been removed.
The woman driving the car was unhurt, according to the company.
Severn Trent Water said: "We've managed to get some people back on supply following this morning's burst pipe in the village of Epperstone, north of Nottingham, but there's still more to do.
"Due to the size of the water pipe affected, a lot of villages and towns in the area have been affected by the issue and left without water.
"We believe the affected areas include Radcliffe on Trent, Bingham, East Bridgford, Upper Saxondale and Flintham, and we'd like to apologise to everyone who's had problems this morning."
The company said that it was looking at other ways to get water out to residents, particularly what it described as "our most vulnerable customers".
Meanwhile, customers asking online how long supplies might take to be restored were being told by the provider: "I cannot give a time scale - we are looking at all options for getting customers back on supply."
A spokesman said the fault set off a low-pressure alarm at about 4.50am and engineers quickly discovered the exact location due to the localised flooding.
The main is a large 24-inch (60cm) diameter pipe, which Severn Trent was able to isolate in order to initially put a few thousands home back on supply.
To restore supply to the remaining customers, engineers are now having to excavate the scene, and pump out the excess water in order to get at the breach.
The spokesman said the worst case scenario was a new length of pipe would have to be fitted, and put the time of any repair at "hours" without placing an exact figure on the works needed.
Severn Trent said it was in the process of contacting vulnerable people on its register, including those requiring kidney dialysis and other medical conditions, in order to get bottled water out to them quickly.
The spokesman said: "We've a register of the most vulnerable people and places, like hospitals - although I don't believe any hospitals are affected - where we can get bottled water, or bowsers or tankers if it's appropriate, out to them.
"We're not quite at the point of getting bottled water out to everyone but we understand people's concerns and our engineers are working as quickly as they can to restore supply."
It is not yet clear what caused the burst.
Severn Trent said residents could contact the company on 0800 783 4444 or tweet @stwater.