NEW YORK (AP) - About a third of New York City's subway lines were suspended for more than an hour during a busy, hot Friday evening commute, stranding some passengers underground and sending others searching for other ways home.

The stoppage affected the No. 1, 2, 3, 4, 5 and 6 trains that serve swaths of Manhattan, the Bronx and Brooklyn. It also halted the S shuttle train that links Grand Central Terminal and Times Square - two of the city's busiest stations.

The Metropolitan Transportation Authority warned that there would still be "extensive delays" in the system, which serves more than 5 million people per day, even after service began to resume Friday night. It blamed the suspension on a network communications problem.

The temperatures was still 91 degrees Fahrenheit (33 degrees Celsius) on Friday evening when the stoppage happened, though meteorologists estimated that it felt like 100 degrees, leaving riders sweating in stopped trains with doors closed. The breakdown came as the city gears up for scorching temperatures throughout the weekend.

MTA officials were not able to immediately determine the cause of the breakdown, which started at about 6 p.m.

The state agency that runs the city's subway system urged passengers to remain in train cars while crews work as quickly as possible to bring people into stations.

At the World Trade Center No. 1 line station, a clerk issued refund tickets and directed people to other nearby lines. Passengers - many of them visitors to New York - seemed to take the developments in stride.

"It's about what I expected," said Derek Lloyd, who's from Hanover, Massachusetts, near Boston and its transit system. "I don't know that ours is much better," he said with a smile.

On one line that was running, passengers packed into one car that didn't appear to have air conditioning. Sweat glistened on riders' skin as they sought relief, fanning themselves and one another.

One woman noted, "This is dangerous."

It was the second time in the past week that New York subway riders got stuck underground. Last Saturday, a power outage that stretched across 30 Manhattan blocks from the Upper West Side to Times Square left passengers stranded till trains were manually moved into stations and doors opened. The outage was blamed on a system that failed to isolate a faulty distribution cable.