A city crew was responding to the location to shut down water in the area, Boughton said.
"Serious water main break on North Street," the mayor said in a second Tweet. "City lost millions of gallons of water. We'll be working around the clock to repair."
The repair work was expected to take approximately six to eight hours, he said. It was not clear how many water customers were affected, but one Facebook post indicated "muddy" water in the area.
Drivers should expect delays in the area.
There is ongoing construction work in Danbury on North Street near Interstate 84.
Click here to follow Daily Voice Danbury and receive free news updates.