A man stopped for an expired car registration sticker traded gunfire with police Tuesday during a highway chase that ended with a fiery crash involving a school bus and a trooper with a gunshot wound in his shoulder, police said.

Trooper Patrick R. Casey suffered a "flesh wound," state police Capt. James Raykovitz said.

Two people who were in the car when it was stopped were in custody, but Philadelphia police were searching for two more following the midmorning crash on a downtown highway, authorities said.

When police first stopped the car, they asked the four people inside to exit the vehicle, but one of the suspects jumped back in and took off, investigators said.

Trooper Patrick R. Casey, providing backup, pursued the car, at one point getting in front of it to try to force a stop, authorities said. The suspect instead rammed Casey's cruiser, then pulled alongside him and opened fire, Raykovitz said.

The suspect then crashed into the school bus, causing both vehicles to burst into flames. The bus was empty except for the driver, who escaped unharmed. The suspect again started shooting, while Casey returned fire, authorities said.

Casey, 31, was struck once in the shoulder.

Casey was in good condition later in the day, discussing holiday plans during a phone call with Gov. Tom Wolf.

"The governor was glad to hear that Trooper Casey believes he will be able to be home with his family for Thanksgiving," Wolf's office said in a statement.

Steve Glowacki was working nearby when he saw the shooting.

"I saw a gunfight down here," he said while pointing to Interstate 676 from an overpass. "I came out, there were cops down there, shooting at someone, and then someone was shooting at them."

He said he saw state police troopers with guns drawn.

"I heard what I thought was gunfire, and it turns out that it was," he said. "When I came out, there was a gunfight going on and that car had already hit the bus."

Video posted on social media shows law enforcement officers earlier Tuesday running down the closed section of I-676 and apprehending one man.

Some good Samaritans were also involved in the capture of the suspects, authorities said.

The busy stretch of road was closed in both directions between Interstate 76 and Interstate 95, but it reopened later in the day.

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