Phoenix firefigters are expected to work into Friday evening to contain a blaze at a west Phoenix warehouse that was fueled by thousands of piled up wooden pallets.

The four-alarm fire has forced the closure of Buckeye Road in both direction at 51st Avenue, authorities said. Hundreds of pallets caught fire and began an intense blaze at the warehouse, near 59th Avenue and Buckeye, sending flames high into the air. Around 3 p.m., a 12 News camera crew aboard a helicopter caught on film a section of a wall collapsing onto a parked car.

Popping sounds could be heard periodically, believed to have been set off by exploding propane tanks inside the building.

The area is home to several businesses, including Knight Transportation Inc, the owner of the property where the fire began.

Greatwide Distribution Logistics, a warehouse and distribution company, was housed inside the building. Phoenix Fire Division Chief Mike Sandulak told 12 News that fire crews are fighting the blaze in defensive mode, trying to form a perimeter around it and preventing it from spreading to nearby businesses in the largely industrial and commercial area. Crews are fighting parts of the blaze with giant streams of water atop ladder trucks and letting other sections of the fire burn itself out. Authorities are keeping an eye on at least one building nearby that contains pool chemicals; a hazardous-material team is on scene as a precaution. They're also concerned because of the afternoon heat - it was about 104 degrees at 3:15 p.m. - and the health risks that poses for firefighters.

Bob Kard, an air quality official with Maricopa County, told 12 News that early tests show there's no environmental impact, in part because the hot weather is lifting the smoke high up into the air. He cautions that people who live or work in the area to either leave the area or stay indoors nonetheless.

It's not immediately clear what started the blaze or how long a stretch of Buckeye Road is closed, or when the freeway will be reopened to traffic in that area. More than 100 firefighters reportedly are on scene.

The warehouse is several miles away from Sonoma Pacific of Arizona, where a suspicious fire in mid-July burned through piles of wooden pallets and spread to parked semi-trailers at a neighboring trucking company. That surrounding area is a mix of homes, business and industrial yards.