PORTLAND — A water main break is affecting traffic on a street in the Rosemont area.

The break is at 12 Bancroft St., near the intersection of Brighton Avenue. Traffic on Bancroft Street is affected, but not traffic on Brighton Avenue, according to Michelle Clements, a spokeswoman for the Portland Water District.

It’s not clear what caused the break, which happened around 4 a.m., she said. Water flow has been reduced and the district is preparing to excavate, she said.

About 30 water customers are affected by the break.