Diamond Pet Foods in Lathrop, Calif. was rocked with an explosion Sunday evening September 23,...

LATHROP — An explosion at the Diamond Pet Food facility early Sunday morning burned three employees seriously enough for them to be flown to the University of California, Davis, Regional Burn Center, fire officials said.

Further information about their condition was not available. Lathrop-Manteca Fire Protection District Battalion Chief Gene Neely would not release the names of the injured.

Neely said employees were welding in the tower of the facility, at 250 Roth Road, when an explosion occurred about 1:30 a.m.

The exact cause is still under investigation, but Neely said, "We believe that the welding operations in connection with the dust from the dog food caused the explosion in the tower."

The fire also caused minor structural damage to the tower's tin siding, Neely said.

James Monty, chief of the Lathrop-Manteca Fire District, said the biggest job was not putting out the fire but staying on the scene to make sure no other blazes erupted.

On Monday morning fire crews were at the site to conduct safety checks.

Officials of the Meta, Mo.-based manufacturer of dog and cat food did not return phone calls.