The chopper was taking off from a helipad at the KOMO-TV station when it went down on Broad Street downtown and hit three vehicles, starting them on fire and spewing burning fuel down the street.
Kristopher Reynolds, a contractor working nearby, saw the wreck. He said the helicopter lifted about 5 feet and was about to clear a building when it tilted. It looked like it was trying to correct itself when it took a dive.
"Next thing I know, it went into a ball of flames," he said.
KOMO identified the pilot as Gary Pfitzner. The other man killed was Bill Strothman, a former longtime KOMO photographer who was working for the helicopter leasing company.
Strothman was someone "who really knew how his pictures could tell a million words," news anchor Dan Lewis said on the air. "He was just a true gentleman."
"We're going to miss you guys. And thanks so much for all that you gave to us," Lewis said, choking up.
Firefighters who arrived at the scene before 8 a.m. found a "huge black cloud of smoke" and two cars and a pickup truck engulfed in flames, Seattle Fire Department spokesman Kyle Moore said.
Fuel running down the street also was on fire, and crews worked to stop the fuel before it entered the sewer, Moore said.
An injured 38-year-old man managed to free himself from a car and was taken to Harborview Medical Center, Moore said.
The man suffered burns on his lower back and arm, covering up to 20 percent of his body, hospital spokeswoman Susan Gregg said. He was in critical condition in intensive care and likely will require surgery, she said.
Two others who were in cars that were struck by the helicopter were uninjured.
A woman went to a police station and talked to officers. A man from the pickup walked off to a nearby McDonald's restaurant, and police later located him unhurt, authorities said.
Only the helicopter's blue tail end could be identified among the wreckage strewn across the lawn in front of the Seattle Center, a popular spot for tourists and locals that hosts many festivals and sporting activities. National Transportation Safety Board investigators inspected the scene.
The cause of the wreck is not yet known. Mayor Ed Murray said the crash site could be closed for three to five days while officials with the NTSB and Federal Aviation Administration probe what happened.
The station said the Eurocopter AS350 helicopter might have hit the side of a building before it went down.
Lewis said it wasn't the regular KOMO helicopter but a temporary replacement for one that is in the shop for an upgrade.
Workers at KOMO rushed to the window when they heard the crash. Reporters with the station were then in the position of covering the deaths of colleagues.
On the street shortly after the crash, KOMO reporter Denise Whitaker said: "It is definitely a tragic scene down here. It is a difficult time for all of us this morning."
The crash site also is near the EMP Museum, the music and culture museum created by Microsoft co-founder Paul Allen.
The Seattle Monorail, which runs about 50 yards away, was operating Tuesday morning and passed the scene about 15 seconds before the crash happened, said Thomas Ditty, the monorail's general manager.
Other cities have experienced helicopter crashes as TV stations rush to cover the news from above major cities.
Two news helicopters collided in midair in Phoenix in 2007 as the aircraft covered a police chase, sending fiery wreckage plummeting onto a park. Four people in the helicopters were killed.
The crash prompted changes at the stations in how they operated their helicopter crews.
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