A four-alarm blaze erupted beneath the elevated Metro-North tracks in East Harlem Tuesday evening, creating a dismal situation for commuters heading into Manhattan Wednesday.

The damage halted Hudson-, Harlem- and New Haven-line service into and out of Grand Central Terminal.

An MTA spokesperson said after midnight that all Manhattan-bound Metro-North trains would operate on a Saturday schedule on Wednesday and terminate in The Bronx.

From there, passengers would have to take subways into Midtown.

The fire erupted just after 6:30 p.m. Tuesday at a garden nursery at East 119th Street and Park Avenue.

It spread to construction debris and several trailers, fire officials said.

The elevated structure was ­affected, and structural engineers were called in to assess damage.