NJ Transit and Amtrak service was suspended just before 3 p.m. on Thursday due to power issues.
Rail service into and out of Penn Station has resumed, but is subject to up to 30-minute delays.
Midtown Direct trains are no longer being diverted to Hoboken.
Significant delays continue due to rail congestion and single-tracking.
A malfunctioning circuit breaker caused the widespread issue, resulting in a loss of power on the tracks between New York Penn Station and Newark Penn Station.
"I am so angry and hot," said commuter Cheryl Gaddsen. "When the weathers is hot or cold, the trains are always messed up."
Amtrak first reported the outage just before 2:45 p.m.
An unrelated brush fire in the area complicated the repairs, according to NJ Transit.
NJ Transit rail tickets and passes were being crossed-honored by NJT and private carrier buses and PATH at Newark Penn, Hoboken and 33rd Street, New York.
Customers should visit njtransit.com/ABC for alternate service information.
This is the latest in a string of incidents that have adversely impacted rail commuters. On Tuesday, NJ Transit and Amtrak commuters experienced delays and cancelations due to overhead wire problems in the morning and later a stalled train outside Penn Station.
Earlier Thursday, Amtrak had already warned customers in the Northeast that they may face up to 60-minute delays for the rest of the week because of the high temperatures.
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