(CNN) -- Two tractor-trailer trucks crashed and burst into flames Thursday on a bridge between the United States and Mexico, shutting a key border crossing and killing four people, police said.

Police look at the aftermath of a fiery crash on a bridge linking Reynosa, Mexico, and Pharr, Texas.

The collision on the Pharr-Reynosa International Bridge in Texas triggered a chain-reaction accident with three other vehicles, said Lt. Lupe Salinas with the Pharr Police Department.

A pickup flipped off the bridge, killing three people. Another person died in a vehicle that struck one of the tractor-trailers. Six others were injured.

Pharr Emergency Management Coordinator Elsa Sanchez told The Associated Press the pickup truck had Texas license plates, and the two 18-wheelers and a minivan involved in the wreck appeared to have Mexican plates.

The accident happened around 7:30 p.m. (8:30 p.m. ET). The bridge was closed for the rest of the evening, but Salinas said he expected it to reopen Friday morning.

"As far as we can tell, there is no damage," Salinas said, "but engineers will inspect it and let us know."

The bridge is normally open from 6 a.m. until midnight and is closed overnight.

The 3.2-mile-long bridge connects U.S. 281 in Pharr, Texas, to the city of Reynosa in the Mexican state of Tamaulipas, according to the city of Pharr's Web site. On an average day, the site says, 5,800 vehicles cross it.

http://www.cnn.com/2008/US/01/11/border.fire/index.html