MODESTO (CBS13) — Firefighters say an early morning fire at a pallet yard went to four-alarms on Friday.

The scene is along the 1700 block of Reliance Street in Modesto.

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The fire was still smoldering through the morning hours.

Modesto Fire says the incident, which started just before 3:30 a.m., prompted a four-alarm response. Firefighters from Modesto, Ceres, Turlock and the Stanislaus Consolidated Fire Protection District responded.

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Firefighters were able to contain the flames to the yard, officials say.

Exactly what started the fire is now under investigation.

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Crews remain at the scene through the early morning hours as the fire smolders.