[UPDATE BELOW]

A Nassau County police officer was killed earlier today during a shootout on the Cross Island Parkway in Queens that also left one suspect dead. The unidentified officer, who worked with the Emergency Services Unit, was shot once shortly after 11 a.m. and pronounced dead at North Shore Long Island Jewish Hospital. One source tells the Wall Street Journal that the officer had "pulled a car over at about 11:10 am at the entrance ramp to the parkway at 241st Street and Jamaica Avenue."

In addition to the fatally shot suspect, police are searching for a second suspect, who remains at large, and the Cross Island was closed in both directions because of the investigation. The shooting took place right on the border between Nassau County and Queens, near the Belmont Race Track. It's still unclear what prompted the shooting or the traffic stop, but we'll update as more information becomes available. A spokesperson for the Nassau County Police Department tells Newsday, "We're trying to sort it out."

Update 4:09 p.m.: Police sources tell the Post that the officer, identified as Artie Lopez, had pulled over a vehicle that matched a hit-and-run driver in Nassau County. Paul Walcott, a music producer from Bayside, Queens, witnessed the traffic stop from a nearby gas station and tells the AP, "The officer's walking up to the car. They just pulled out (a gun) and shot. He went right down. He got hit point blank. He went straight down. In broad daylight, this time of day, it was incredible to see something like that."

The traffic stop occurred at the southbound entrance ramp to the parkway, near a Mobil gas station. Brandon Ramos, who works near the location, tells Newsday, "As I was walking upstairs, I heard a huge boom. I ran outside and I saw a cop lying on the floor, on his back, and the other officer was administering CPR... He was shot in the chest. He was motionless. The other cop looked really distraught."

The suspect sped off, but the vehicle already had four blown tires, and sources tell the Post "he ditched his ride and car-jacked another vehicle near Hempstead Avenue and the Cross Island Parkway, where he fatally shot the driver." He subsequently ditched that vehicle in Cambria Heights and fled on foot. He remains at large.