At least six subway lines shut down Saturday morning due to “a communications issue,” leaving passengers stranded in trains and sweltering on stifling platforms.

“We are troubleshooting a network communications issue that is impacting service on lines 1-6,” the official New York City Transit Subway Twitter account, @NYCTSubway, posted at 10:37 a.m. “ Right now trains are being held in their stations. The information displayed on countdown clocks may or may not be accurate. We will provide updates as we work to resolve the issue.”

The agency then tweeted a series of directions for riders searching for trains that were operating.

Another post 45 minutes later said some trains were back in service.

By 11:40, the agency said the trains on those lines were moving in the Bronx and Manhattan, but Brooklyn trains were still out of service.

“Update: Service on lines 1-6 in the Bronx and Manhattan is moving again. We’re working to restore our ability to dispatch trains in Brooklyn. We appreciate everyone’s flexibility during this situation and we deeply regret any inconvenience this caused our customers.”

“We are continuing to investigate the cause and will provide a full explanation as we learn more,” the agency said in another tweet. It did not respond immediately to a request for more information.

Its posts were met with a series of angry responses from straphangers.

“By “flexibility” you mean ‘being forced to get a car to my medical appointment because there was no information from crew for more than 15 min?'” tweeted Mary Beth Quirk.

“Oh and losing the cost of my fare.”

Straphanger Katherine Abigail called the holiday weekend snarl “insane.”

“Listen y’all I’ve been trying to get to work for 45 minutes and people are sweating profusely in the lower level of 59th street,” Abigail tweeted.

Others complained that their trains were stuck between stations, leaving them stranded.