US stunt rider Alex Harvill was killed Thursday while training to break the record for the world's longest motorcycle jump, officials in Washington state said. The 28-year-old was practicing to beat the 351-foot (107-meter) milestone when his bike slammed into the top edge of the dirt mound he was using as a landing ramp. Harvill was thrown from his machine, according to local media. The Grant County Sheriff's office said he died later in hospital and that an autopsy would determine the exact cause of the rider's death. Harvill, a father of two, had been due to make his record attempt at an airshow in the town of Moses Lake, 170 miles (275 kilometers) east of Seattle. A professional motocross rider, Harvill had already set a previous Guinness World Record in 2013 with a 297-foot jump from one dirt ramp to another. ban/cjc/jh/ft