Relief may be on the way for at least some frustrated Penn Station riders after another brutal rush hour Friday.

Amtrak late Friday said it expects to reopen its East River tunnels at 5 a.m. Saturday. They had been closed since a Thursday morning fire set off a cascade of delays for Long Island Rail Road, NJ Transit and Amtrak.

The Long Island Rail Road, NJ Transit and Amtrak are operating on limited service Friday. NJ Transit said its Midtown direct service will be diverted to the Hoboken terminal. LIRR said most of its trains will be rerouted to Grand Central or Atlantic Terminal, with no westbound service to Penn Station. LIRR also said the rerouted trains wouldn't be reflected in its app, and urged travelers to listen for announcements.

The disruptions come as LIRR prepares its riders for a potential service shutdown starting at midnight. Unions representing LIRR workers are threatening to strike after reaching a stalemate with the MTA over pay raises and work rules.

The Thursday fire broke out in a tunnel connecting the LIRR between Manhattan and Queens. Officials with Amtrak, which owns the tunnels, said the cause of the fire was still under investigation as of Friday afternoon. They did not specify what equipment was damaged or how.

It took more than an hour to extinguish the fire, which led to delays that also backed up Amtrak's own Northeast Corridor service. Amtrak warned Friday its trains heading through the New York area could see delays of about 40 minutes.

This story has been updated to reflect Amtrak's plan to reopen its East River tunnels Saturday morning.