A water main rupture near the Saw Mill River Parkway and McLean Avenue flooded roads, backed up traffic and left about 50,000 people in Yonkers with no or limited water service, officials said.
Morning commuters are advised to use alternate routes.
Westchester County police said the southbound lanes of the Saw Mill River Parkway near the Cross County Parkway was set to remain closed until at least 5 a.m. Tuesday morning. The westbound lanes of the Cross County Parkway, which had been closed after the main ruptured Monday at noon, were reopened at 10 p.m. Tuesday night.
The Westchester County Health Department issued a boil-water advisory at about 5:50 p.m. as Yonkers officials said they would be issuing continuing advisories, including information on where water stations will be set up for residents. The boil-water advisory was issued for people and businesses in the area from the New York City line to Ashburton Avenue and the Hudson River to the Saw Mill River Parkway
About a quarter of Yonkers -- the entire southwest quadrant -- was affected by the outage, including Saint Joseph's Medical Center. Some customers lost water service entirely, and others had reduced water pressure or discolored water.
"Know that we are working, [that] we are attempting to isolate the problem," said Yonkers Mayor Mike Spano at a late-afternoon news conference at the city's Office of Emergency Management. "It's all hands on deck here."
Water distribution stations are being planned for the affected areas on Tuesday.
Spano said he hoped the problem could be resolved within 24 to 48 hours.
The 30-inch main ruptured around noon Monday when it was struck by an outside contractor laying fiber-optic cable along the Saw Mill River Parkway north of McLean Avenue, officials said.
"We've gone into disaster mode," said Dean Civitello, a spokesman for Saint Joseph's Medical Center. Though the 194-bed hospital has plenty of drinking water, he said nonpotable water used for flushing toilets, air-conditioning units and boilers was being provided by tankers through the Yonkers Fire Department.
In addition, St. John's Riverside Hospital in Yonkers is experiencing low water pressure.
Spano urged residents and businesses to conserve water, and said work crews were trying to assess the size of the hole in the century-old main and how long a repair might take.
"We're attempting to isolate the portion of the main that is broken," he said. "Once we can isolate that, we can potentially divert water to the areas that are affected."
Officials also said that tankers from neighboring municipalities might be used to supply the city's needs.
Flooding on the Saw Mill also snarled Monday afternoon's commute.
"It's continuing as the rush hour progresses, but traffic is actually moving pretty well going north on the Saw Mill," said Kieran O'Leary, a spokesman for the Westchester County police, early in the evening.
Floodlights were brought in around 6 p.m. to allow city DPW workers to work in the area through the night.
O'Leary said the main rupture has caused traffic delays on the southbound Saw Mill River Parkway and the westbound Cross County Parkway. Southbound traffic on the Saw Mill River Parkway was being diverted onto Rumsey Road in Yonkers, while westbound Cross County traffic was being funneled onto Central Park Avenue.
The outage caused traffic disruptions on the parkway southbound from Rumsey Road and the Cross Country Parkway west of New York State Thruway.
Residents can call 914-377-4357 for more information.