Workers were stripping paint from the façade of the Port Authority Bus Terminal just after 11:00 a.m. when fumes from the project wafted into an adjacent office building on West 42nd Street.
Dozens of employees in the office building smelled the fumes. Around 100 people were evacuated.
Four of them were taken to Bellevue Medical Center for observation. Others were treated at the scene.
The paint work was stopped and the fumes dissipated. Workers returned to the building shortly after 12:00 p.m.
West 42nd Street was briefly closed between Seventh and Ninth avenues.