Houston health officials ordered a mandatory boil water notice for the entire city Friday after a break in a pipe that provides 50% of Houston's water on Thursday sent drivers on a flooded freeway scrambling onto the top of their cars.

Restaurants were ordered to cease operations immediately and many schools and business shut down for a second day Friday.

The boil water notice was in effect for the city's entire fresh water system.

“This was a major, a major break,” Mayor Sylvester Turner said at a Thursday afternoon news conference. “As you can see it produced a lot of water and it is still producing a lot of water.”

Turner told reporters that private contractors, attempting to repair a minor leak, were moving soil around the 96-inch water main in east Houston when it broke around noon Thursday.

“The closer they got to where the leak was occurring, removing the soil, the line simply erupted,” Turner said.

He said the 35-year-old pipe provided as much as 50% of the city's water.

Firefighters rescued three people after more than a dozen cars were trapped on the city's 610 East Loop.

Fire chief Samuel Peña also said tanker trucks were deployed around the affected areas of the city because of concern that lower water pressure could disrupt normal firefighting capabilities.

All of Harris County courts were shuttered Friday along with schools in the Houston Independent School District. The University of Houston and Texas Southern University closed Thursday.

Four early voting locations were closed until further notice, according to Harris County Clerk Diane Trautman.

“When you are dealing with an aging infrastructure, you are going to have these main line breaks,” Turner said. “And in some cases they are major arteries and can cause a major disruption.”

Contributing: Associated Press