The main broke on Jerome Avenue, near East 177th Street, just before 6:30 a.m.
A torrent of water quickly flooded the area, buckling the street.
The water flowed south to the Cross Bronx Expressway, where an entrance ramp was flooded. Traffic in the area came to a standstill.
Crews shut off the main, but the neighborhood remains a soggy mess. Jerome Avenue was under water for at least five blocks, and the water also made some side streets inaccessible.
The break in the 108-year-old main took nearly three hours to shut off because it supplies so much water to the entire city. Despite the extensive damage to the 36-inch main, water service along Jerome Avenue was not disrupted.
However, Jerome Avenue between 176th Street and East Tremont Avenue is expected to remain closed for a couple of days for repairs.
No. 4 trains are operating normally again.
There are still delays and detours on BX32 and BX36 buses.
There are also concerns about the structural stability of many of the flooded business. Inspectors will be taking a close look at each building to make sure it's safe.