The MTA aims to restore full Metro-North service Friday after a massive East Harlem fire damaged the above-ground rail line.

The four-alarm blaze started around 6:42 p.m. Tuesday near the Urban Garden Center located below Metro-North’s elevated rails at Park Avenue and 118th street, when fuel accidentally spilled on a hot generator during a refueling, according to FDNY officials.

Metro-North crews are working around the clock to make temporary repairs to a section of the railroad’s Park Avenue viaduct that was damaged by the flames, which includes one steel support column and three horizontal steel girders, according to the MTA.

While the railroad’s four tracks remained undamaged, the MTA said structural support and repairs have limited the agency to operating on two tracks, with trains reduced to 30 mph, half the usual speed.

On Thursday, all three Metro-North lines will run on an “enhanced” Saturday schedule that will bring additional trains during peak travel periods. The MTA says this can serve 75 percent of ridership capacity.

Still, customers are urged to explore transferring to and from nearby subway station uptown to avoid the congestion near the repair work. The MTA is cross-honoring Metro-North tickets. NJ Transit is cross-honoring Hudson Line tickets on the Port Jervis and Pascack Valley Line trains.

The Urban Garden Center is a tenant of the New York City Economic Development Corporation and part of the East Harlem community marketplace La Marqueta.

“NYCEDC is currently supporting FDNY in its investigation of the incident,” said NYCEDC Spokesman Anthony Hogrebe in a statement. “All EDC tenants are required by lease to adhere to all relevant laws and regulations. If anything is found to have been in violation, we will take swift and appropriate action.”

Fire department investigators determined the fire broke out when heat from the generator ignited gasoline fumes, which set ablaze wooden pallets and other debris. More than 170 firefighters responded to the scene as thousands of commuters in Grand Central were left stranded during the tail end of Tuesday’s rush hour. No injuries were reported.