BRONX — An unstable building under construction in the Bronx promoted the evacuation of nearby apartments and snarled the morning commute for riders along multiple subway lines.

A contractor called police about 6 a.m. Thursday to say the building at 1232 Southern Blvd. was unstable and possible cracking noises were heard coming from inside, according to FDNY.

Authorities evacuated at least nine buildings in the area but residents have since been let back into their homes, FDNY said.

The building, a $45 million charter school project, is perched next to elevated subway tracks, creating a mess for commuters who need to travel through the Freeman Street stop. Delays were felt throughout the Bronx, Manhattan and Brooklyn.

Nos. 2, 5 and 6 trains were halted or had their routes changes because of the investigation. Shortly before 9 a.m., trains were running again with residual delays.

Shuttle buses and Metro-North cross-honoring were alternate options for commuters while service was stalled.