The cause of the break was unclear. The authority said on Twitter that it was outside of its system and near the street level. The subways were suspended after water rose more than a foot above the rails.

New York City Transit crews were alerted around 7:50 a.m. that a city-owned water main erupted, said Sally Librera, senior vice president of subways for New York City Transit.

The water main was shut off by the city Department of Environmental Protection around 9 a.m., she said. A department representative could not be immediately reached.

“New York City Transit rapidly responded by deploying resources in the Infrastructure, Track and Signals Departments, as well as pumping equipment and supplies to the scene,” Ms. Librera said.

Signal equipment, a power substation and third rail cables were being inspected.

Commuters had a difficult time navigating the disruptions as trains were delayed, streets were blocked and larger crowds than usual waited for buses.