A massive fire engulfs an apartment building construction site. Source: AP

No injuries were reported but the gigantic flames near a downtown freeway interchange could be seen for miles and billowing clouds of smoke closed down adjacent highways in two directions.

The fire damaged buildings and shut down freeways, causing traffic chaos for morning commuters. Source: AFP

More than 350 firefighters fought the blazes, with 250 at the first inferno that was sparked around 1.20am at a block-long building site, Los Angeles Fire Department Chief Ralph Terrazas said.

“It looked like a bomb had just exploded,” LA fire captain Rick Godinez told the LA Times.

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

The heat was strong enough to burst or crack windows in three nearby buildings that house government offices, including the LA Department of Water and Power.

Three floors of one adjacent building were damaged by fire, and 14 other floors sustained water damage.

Embers spewed across the freeway, igniting scrub and charring a traffic sign.

Portions of US Route 101 and Interstate 110 were shut down for a while as burning debris fell into lanes.

LA County firefighters battle the inferno next to the 110 Freeway. Source: AP

Streams of water soared through the sky from massive hoses. Source: AP

Los Angeles County firefighters on the scene as the fire rages in an apartment building. Source: AP

Los Angeles County firefighters at the scene of the first fire. Picture: AP Source: AP

Commuter traffic remained jammed long after rush hour, with vehicles backed up for miles even after the freeways reopened.

No injuries were reported. The burned construction site was to be a 1.3 million-square-foot residential building — one of a series of large complexes that have gone up in recent years.

The site was still smouldering by late morning, and downtown was littered with ash.

Shortly after 4am, another large fire was reported at a mixed-use building undergoing renovations about two miles 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.

Traffic on State Route 110 was congested for hours. Source: AP

Eerie scenes at the destroyed apartment complex. Source: AFP

LA firefighters and state highway workers watch an apartment building smoulder. Source: AP

Rubble and debris spread for a whole city block, nearly a million square feet. Source: AFP

Workers survey damage at a seven-storey apartment building. Source: AFP

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

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

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

“When you look at the magnitude of this fire, and what we were able to save, it’s amazing,” LAFD spokesman Jaime Moore told Fox 11 television.