Police evacuated the massive Capitol Visitor Center near the end of visiting hours Monday after finding an unattended bag at its entrance. An investigation found nothing hazardous.

A suspicious package was reported about 3:30 p.m. EDT, Capitol Police said in a news release. Fire trucks and other emergency vehicles were called and an evacuation with street closures was undertaken "out of an abundance of caution," police spokeswoman Sgt. Kimberly Schneider said. The area was reopened to vehicles and pedestrians shortly before 6 p.m.

The underground visitor center opened in December. At 580,000 square feet, it is three-quarters the size of the Capitol building itself.

Nearly 3 million people visit the complex each year. It's not uncommon for tourists to accidentally leave belongings behind.