(CNN) -- Police closed a section of Interstate 90 in eastern New York on Saturday after a gunman opened fire at a state trooper after a traffic stop, authorities said.
A law enforcement officer approaches the gunman Saturday along Interstate 90 in New York.
A witness said the scene was "chaos" as drivers and passengers ducked to avoid the shots and attempted to flee.
The incident occurred about 11:55 a.m. near the town of East Greenbush, just southeast of Albany, the New York State Police said in a statement.
"A large contingent of state police and East Greenbush PD responded to the area," the statement said. "The traffic on I-90 was evacuated, and I-90 was closed down in both directions in Rensselaer County."
The gunman was shot and is in state police custody, authorities said. However, a section of I-90 between two exits, where the incident occurred, remained closed Saturday afternoon.
The Albany Times Union reported on its Web site that the gunman was in a hospital, although it was unclear whether he was shot by police or turned the gun on himself. No officers were injured, the newspaper said.
The gunman's condition was not immediately known.
"It was chaos," said witness Carol Winn, who said she was headed to Albany on I-90 "when all of a sudden there was this big traffic jam in front of me." Watch scenes from Saturday's incident »
Winn said, "I heard a shot fired, and then I thought maybe there was a deer in the road and someone had to shoot it to put it down. But then I heard more shots and saw people ducking down in their cars, and I knew something was wrong."
She said a trooper with his gun drawn walked beside her stopped car as she heard more shots. Along with other drivers, Winn fled the scene on foot.
"There was maybe 100 people running south on the northbound lane, and as we were running, we heard shots continuing to be fired," she said. Winn estimated that the shooting was taking place about 15 cars in front of her.
"I got in a car that was going south, and they got us to safety," she said. "I never got a chance to look at the shooter, but someone else that fled with me said he saw someone get out of a taxi cab with a rifle."
Winn estimated hearing about 10 shots in all.
Video footage shows the gunman standing outside what appears to be a taxi holding up a rifle as numerous police cars respond to the scene and other cars are stopped some distance away. A helicopter hovered overhead.
Winn said Saturday afternoon that she was headed back to get her car, which was abandoned in the road, since that section of interstate had been reopened.
"I still have the keys in my hand, but I left my purse," she said. "I didn't care about my purse. I just left it there and ran."
CNN's Nick Valencia contributed to this report.
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