Janesville police and water utility crews are on the scene of an 8-foot wide water main break on Van Buren Street just east of Main Street.
Police said the water main break is 8 feet in diameter, and when the water main initially broke around 1 p.m. a column of water 40 to 50 feet high was shot into the air.
The water then rushed down the hill toward Main Street, which caused flooding, officials said. Officers are on the scene directing traffic while the water utility crews work on shutting off the water.
Officials believe the break is weather related, but are not sure how long it will take to clean up the water or fix the break.
Police did not know if residents and businesses in the area are without water.