Firefighters raced Wednesday to get the upper hand on a wildfire in the brush-covered hills of sprawling Griffith Park but rising temperatures and low humidity threatened to stifle their progress.

The danger to homes south of the park, where the fire erupted Tuesday afternoon, had eased and many of the hundreds of residents evacuated overnight were allowed back in their homes Wednesday morning. Fire officials warned things could change throughout the day.

"The canyons and those erratic winds are dangerous," said fire Capt. Carlos Calvillo.

Cooler temperatures overnight and continuous water-dropping by helicopters helped hundreds of firefighters get the 600-acre blaze about 40 percent contained by dawn.

The weather reprieve was expected to be short-lived, however. The National Weather Service said Wednesday's temperatures would push into the 90s again, with humidity levels hovering around 5 percent.

"As things heat up during the day, there are serious concerns things could flare up," said fire Capt. Ron Myers.

Stoked by extremely dry, hot conditions the fire quickly spread through the park Tuesday, forcing closure of several major attractions, including the recently renovated Griffith Park Observatory and the Greek Theater. Animals at the Los Angeles Zoo inside the park were moved indoors, and some 300 residents in the Los Feliz neighborhood were evacuated.

The cause remained under investigation. Mayor Antonio Villaraigosa said there were "no facts" to indicate the fire was intentionally set.

Police and fire officials offered differing opinions about a man found badly burned near the origin of the fire.

David Schaefer, a fire department paramedic who treated the man for second- and third-degree burns, said the man fell asleep while smoking a cigarette and "woke up with his shirt on fire."

Fire investigators remained interested in the man as the possible source of the fire, Calvillo said. But police Sgt. Lee Sands said the department was finished questioning the man and did not consider him a "person of interest."

Authorities dispatched 13 water- and retardant-dropping aircraft to douse hotspots in the park — a mix of wilderness, cultural venues, horse and hiking trails, and recreational facilities set on more than 4,000 acres on the hills between Hollywood and the San Fernando Valley.

The fire destroyed Dante's View, a trailside terraced garden on Mount Hollywood. "This is a tragic sunrise," City Councilman Tom LaBonge said Wednesday morning while surveying the damage.

"You look right there and you'd think you were at the Observatory looking at Mars. It's burned to the ground," he said.

The flames and smoke also forced officials to put most of the zoo's 1,200 animals inside holding quarters.

"So far the animals are faring fine," said Jason Jacobs, director of marketing and public relations for the zoo. "I haven't heard any reports of anything going wrong."