A security guard and two others were shot on Wednesday inside the US Holocaust Memorial Museum in downtown Washington, authorities said.

Police said a gunman armed with a rifle opened fire on the security guard and that other security guards returned fire. The gunman was reported wounded.

The shooting was reported at 12.52 pm, and officers rushed to the scene just south of Independence Avenue.

DC Fire Department spokesman Alan Etter said there was no immediate information on the shooter. He said two men were transported to a hospital with “serious” gunshot wounds.

One witness, Dave Unruh, of Kansas said he was waiting to enter the museum when he heard one gunshot, then a sequence of four or five gunshots. He said he then heard someone scream, “Hit the floor!”. He and his wife, Karen, and their two grandchildren hit the floor and were herded out of the building by authorities. Unruh called the experience “intensely, extremely frightening”.

By 1 pm, the street in front of the museum was blocked by a police officer. A group of schoolchildren was rushed onto a chartered luxury coach and the bus driver struggled to pull away from the block. The mother of a Massachusetts teenager said students on a school trip to the museum heard gunshots before they were evacuated from the building.