RIDGEFIELD PARK - Hundreds of people had to be evacuated from an office building today after they reported they felt the floor shake.

The Ridgefield Park building had about 500 people inside.

Around 9:30 a.m., workers on the fifth floor say the building started to shake.

Firefighters came to check the building and its utilities but couldn't find a reason as to why the building would shake.

"We cannot come up with a cause at all. We have no idea what caused it. There's no reports of seismic conditions in the area," says Douglas Hansen, of the Ridgefield Park Fire Department.

Authorities called in a structural engineer to inspect the building.

The building was later deemed safe and everyone was allowed to return.