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Truck drivers delivering replacement portable buildings stop to look at the burned shells of other portables at James Madison Elementary School in San Leandro, Calif. Friday, April 26, 2013. (Laura A. Oda/Bay Area News Group)

SAN LEANDRO -- Arson is suspected in an early-morning fire Friday that destroyed six new portable school buildings that were to house offices for the San Leandro school district, authorities said.

The blaze, reported shortly after midnight Friday on the James Madison Elementary School campus at 14751 Juniper St., shot flames and smoke high into the air, authorities said.

Police and fire investigators are treating the fire as suspicious because the portables were delivered to the school earlier this week and the utilities had not been connected, said San Leandro police Sgt. Derrel Ramsey.

"There's no water, no gas, no electricity," he said. "So obviously what makes it suspicious is what started it -- unless there was oil in there or another substance that spontaneously started, but that's reaching. We'll do our investigation and (Alameda County Fire) will do theirs, but clearly, it's a suspicious one."

No one was injured. The fire was extinguished in about 20 minutes, said a fire department spokeswoman. The buildings destroyed were intended to be used as district offices, and all the buildings that house classes at James Madison Elementary were spared.

The school was open as usual Friday morning.

Police said they have no suspects or reports of anyone seen near the buildings when the fire began.

Staff writer Kristin J. Bender contributed to this report. Contact Rick Hurd at 925-945-4789 and follow him at Twitter.com/3rdERH.