A commercial helicopter crashed onto a highway and burst into flames late Thursday night, killing all four people on board, emergency officials said. The aircraft was engulfed when firefighters arrived at the scene in western Maryland minutes after receiving a call at 10:30 p.m. EDT (0230 GMT), said Washington County emergency services director Kevin Lewis. No vehicles on the highway were hit when the helicopter crashed in the eastbound lanes of Interstate 70. Troopers have shut down the highway in both directions near the crash site. Lewis, who was among the first emergency responders at the scene, said there are power lines down in the westbound lanes. The crash happened west of the Washington County-Frederick County line, on the western slope of a ridge known as South Mountain. Smithsburg is about 10 miles (16 kilometers) east of Hagerstown. It wasn't immediately clear what brought down the helicopter, which Lewis said was a Robison R44, a four-seat commercial craft. Maryland State police are in charge of the investigation. The National Transportation Safety Board and the Federal Aviation Administration have been notified of the crash, Lewis said.