Costa Mesa firefighters look to remove a giant eucalyptus tree that fell on a car and killed the driver. The tree was planted in a median along Irvine Avenue near the 17th Street intersection. (DON LEACH, Daily Pilot / September 15, 2011)

COSTA MESA — A woman was killed in an apparent freak accident Thursday afternoon when a 50- to 70-foot eucalyptus tree planted in a street median fell on her car as she waited at a red light.

Haeyoon Miller, 29, of Tustin, was pronounced dead at the scene. Cause of death is pending an autopsy.

Authorities have not determined why the tree along Irvine Avenue, near the 17th Street intersection, toppled.

It was not particularly windy, and Newport Beach city officials said the tree was pruned in April and was not diseased.

“We don't know why the tree fell,” said Newport Beach city spokeswoman Tara Finnigan.

Newport Beach workers maintained the tree — the third one from the end of the Irvine Avenue median lined with towering eucalyptus — even though it was on the edge of Costa Mesa's city limits, she said.

Police officers shooed media away from the median, saying they weren't sure the other trees were stable.

Witnesses said bystanders swarmed the scene immediately after the tree fell on the blue 2002 Hyundai Accent GS. The accident blocked all three southbound lanes of Irvine Avenue north of 17th Street.

The victim was initially conscious and talking to people who rushed to her aid, said witness McKenzie Soylula, 16.

Costa Mesa Fire Capt. Fred Seguin said his unit was there in less than five minutes, though Newport Beach authorities were already on the scene.

Seguin said the woman was unresponsive when he arrived.

Witnesses reported that firefighters began lifting the massive trunk, at least 3-feet wide, but “dropped” the trunk back onto the car, which crushed it even further.

Firefighters said that's inaccurate, however.

Authorities said crews used chainsaws to separate the part of the tree on the car from the rest of the trunk. Then, with two braces on either side of the car to keep the trunk from rolling, firefighters used airbags to begin lifting the 9,000-pound section, Seguin said.

A paramedic was inside the car hooking up an IV to the woman while they were lifting the tree section, he said.

While they lifted it, the tree “resettled” and dipped about 4 to 6 inches back on the vehicle.

“At no time did that come down on the patient … and do any pressing injuries,” Seguin said. “It did not come in contact with the patient. It's an operation that, unfortunately, is a slow, safe operation.”

Crews stopped when a Newport Beach city crane arrived to lift the section about an hour after calls flooded into the emergency dispatch.

An emergency medical helicopter en route, which was planning to land at Newport Harbor High School up the street from the scene, was called off when authorities confirmed the driver had died.

“It's just so sad to witness something like this,” said Soylula, a Newport Harbor High student. “They stood around and didn't know what to do. What can you do?”

The tree fell just before 2 p.m. when students were getting out of school and others were grabbing a late lunch at the dozens of restaurants in the surrounding strip malls.

Some witnesses reported hearing a loud “bang” as the enormous trunk flattened the small sedan.

Joanna Clay and Jamie Rowe also contributed to this report

joseph.serna@latimes.com

Twitter: @JosephSerna