Subway passengers were left stranded and broiling on train platforms for more than an hour on Friday night on the first day of a heat wave as several lines in New York City were suspended in both directions.

The Metropolitan Transportation Authority attributed the disruption to a “network communications” issue, and said on Twitter just before 6 p.m. the Nos. 1, 2, 3, 4, 5 and 6 lines and the Times Square shuttle were all affected.

About 90 minutes later, it was reporting that service was slowly being restored. But by that point, passengers and politicians alike had been fuming over the abrupt interruption in service during the evening rush.

The failure, critics said, underscored the problems affecting an aging, troubled mass transit system. The widespread disruption was the second major infrastructure failure in the city in a week. A blackout last Saturday had cut power to the subways, forcing passengers to be evacuated.