Flash floods hit cities and towns south of Boston Thursday as historic rain brought traffic to a crawl and shut down part of I-93.

Boston, Quincy, Brockton, and other South Shore communities are under a flood watch until 9 a.m., according to the National Weather Service.

Portions of Interstate 93, a 190-mile-long highway that connects Massachusetts, New Hampshire and Vermont, were closed because of flooding, the Massachusetts State Police said. Several vehicles were stranded on the highway because of floodwaters, local news media reported.