A Los Angeles city firefighter works amid the ruins of a raging fire that destroyed a massive apartment complex under construction in downtown Los Angeles early Monday, Dec. 8, 2014. It was one of two destructive early morning fires in the city. The other heavily damaged a building that houses multiple businesses in a neighborhood a couple miles away. (AP Photo/Nick Ut)

LOS ANGELES, Calif. - A raging fire that may have been intentionally set Monday destroyed a massive apartment complex under construction in downtown Los Angeles, sending up flames that were visible for miles while raining ash on a large area and snarling rush-hour traffic.

It was one of two destructive early morning fires in the city. The other heavily damaged a building that houses multiple businesses in a neighbourhood a couple miles away.

More than 250 firefighters fought the downtown blaze that was sparked around 1:20 a.m. at a block-long building site, Fire Department Chief Ralph Terrazas said.

Flames consumed the seven-story, wood-framed structure and scorched adjacent high-rises before being brought under control within 90 minutes.

By nightfall, arson investigators had yet to enter the unsafe structure, but fire officials said the fact that the fire erupted so quickly over so much of the building might point to arson. "It's very rare for the entire building to be engulfed at once," city fire Capt. Jaime Moore told the Los Angeles Times (http://lat.ms/1wu0xgF ). "There may have been foul play."

The fire caused an estimated $10 million in losses to the complex, Moore said.

Local and federal investigators planned to examine the debris, check surveillance video from nearby buildings and use special dogs that can detect fire accelerants.

The fire's radiant heat was strong enough to burst or crack windows in three nearby buildings that house city and county offices, including the city Department of Water and Power, which reported cracks in at least 160 of its 10-by-4-foot windows.

Three floors of one adjacent building were damaged by fire, and 14 other floors sustained water damage. That building was closed for the day.

Embers spewed from the fire landed across a freeway, stopping traffic, igniting brush and charring traffic signs.

Portions of U.S. 101 and Interstate 110 were shut down for a time as burning debris fell into lanes. Commuter traffic — slow-moving on good days — remained jammed long after rush hour, with vehicles backed up for miles even after the freeways reopened.

The burned structure, still in the framing stage, was planned to be a 1.3 million-square-foot residential building — one of a series of very large complexes that have gone up around downtown in recent years.

The so-called Da Vinci was to be an Italianate 526-unit complex with amenities such as a pool, full-sized basketball court, library, theatre and business centre.

The developer, Geoffrey Palmer, also built the Orsini and Medici complexes.

"We would like to thank the men and women of the Los Angeles Fire Department for their bravery, swift actions and effective response in putting out the fire," he said, according to City News Service. "... Though we have temporarily lost Building B, we will be opening Building A across the street at the end of January to those families looking forward to occupying their new homes."

Shortly after 4 a.m., another large fire was reported at a mixed-use building undergoing renovations about 2 miles to the west. More than 100 firefighters from multiple agencies responded and had the flames under control in less than two hours, according to Chief Deputy Mario D. Rueda.

One person in a nearby apartment building was treated for minor smoke inhalation, he said.

Around 10 businesses were housed in the two-story structure in the Westlake district, and portions of it were being renovated for residential use.

There were no indications the two fires were connected, Terrazas said.

News from © The Associated Press, 2014