BRAINTREE, Mass. — Drenching downpours quickly turned highways and streets in eastern Massachusetts into rivers, just as traffic started to build for the Thursday morning commute. A large part of Interstate 93 in the Milton-Quincy area was underwater before 7 a.m. as torrential rain moved through.

A flash flood warning is in effect until 9 a.m. for Boston and several communities south of the city, including Brockton, Quincy, and Randolph, officials said Thursday morning. The National Weather Service also issued a flood watch that will remain in effect until 4 p.m. for Rhode Island and eastern portions of Massachusetts and Connecticut.

Heavy rainfall caused areas of flooding on I-93 and other major roadways in Massachusetts on Thursday morning.

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Federal regulators repeatedly granted appeals to remove Camp Mystic’s buildings from their 100-year flood map, as the camp operated and expanded in a dangerous flood plain in the years before rushing waters swept away children and counselors.

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Significant rainfall caused flooding in yet another state as the National Weather Service issued a flash flood warning in Massachusetts Thursday.

Broken tree limbs, twisted metal, crumpled cars and muddy debris remained as crews worked to clear roads and culverts in the wake of Tuesday’s flash flood that killed three people — including two children — and significantly damaged as many as 50 homes, with one home carried away entirely.