4:10 p.m. UPDATE: Fire crews estimate 50,000 pounds of hay were on the truck that caught fire.

SACRAMENTO (CBS13) – Southbound Highway 99 was completely shut down at Florin Road due to heavy smoke conditions Monday after a load of hay caught fire.

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The load was being pulled by a big rig when it caught fire. It’s unknown how the incident happened or whether anyone was injured.

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Authorities urge drivers to avoid the area.