LOS ANGELES (AFP) - A pair of massive fires burst across the Los Angeles skyline early on Monday, damaging four buildings and closing down freeways during the morning commute.

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

City fire officials were unable to give an immediate cause for the blaze, which severely damaged a seven-story apartment building that was under construction.

Damage to the structure appeared to be nearly total. Flames spread for a whole city block, nearly 9.29 square kilometres, officials said.

The apartment development in downtown had caused some controversy in the community due to a pedestrian bridge the developers wanted to erect so residents could avoid street traffic, the Los Angeles Times newspaper reported.

The blaze spread quickly through the building and officials warned there was a risk of building scaffolding falling into the roadway even after the fire was contained.

The fire was so big that responding firefighters could feel the heat from the flames from their fire station, a city information officer said.

Two adjacent office towers were also damaged by the extreme heat. Flames spread to the buildings but were extinguished, officials said.

A second fire a short drive away also caused severe damage to a building housing apartments and commercial spaces that was under renovation.

Both fires were brought under control Monday morning.

More than 350 firefighters battled the blazes, a quarter of the city's firefighting force, Los Angeles Fire Department public information officer David Ortiz said.

Firefighters from nearby areas came in to assist with the response efforts.

"There was a great impact due to both fires on local commute traffic," Ortiz said.