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West Valley City police were investigating a motorcyclist's fiery fatal collision with a semi-trailer rig late Friday morning.

Police Lt. Dalan Taylor said the accident occurred just before 11 a.m. at 4580 S. 4000 West. The motorcyclist was later identified as Jay Nielson, 39, of Holladay.

The semi was northbound on 4000 West when it crashed with the motorcycle in the intersection. It was not immediately known what direction the biker was traveling.

However, upon impact the motorcycle's gas tank burst, spilling fuel, which then ignited underneath the semi, spreading to the big rig and a nearby power pole and grass before firefighters extinguished the flames, Taylor said.

Meanwhile, passers-by stopped and pulled Nielson out from underneath the burning truck and administered CPR.

However, neither they nor paramedics were able to revive Nielson, who was pronounced dead at the scene.

The semi's driver was unhurt.

The cause of the accident remained under investigation. Twitter: @remims