ROBSTOWN, Texas — Six migrants who had crossed the U.S. border from Mexico illegally were killed and five critically injured when a sport utility vehicle that earlier fled Texas police crashed into a drainage ditch, authorities said Wednesday.

The incident began about 10 p.m. Tuesday when police in Robstown, 220 miles (354 kilometers) southwest of Houston, tried to stop the SUV for speeding but broke off the chase when officers lost sight of the vehicle in a brushy area, Robstown Police Chief Erasmo Flores said at a Wednesday afternoon news conference.

Authorities knew nothing of the wreck until about 4 a.m., when a resident called 911 to report an injured man had come to her door, Nueces County Sheriff J.C. Hooper said. Deputies couldn't find the man, but an hour later they encountered two injured young men walking along a road who told of the wreck, Hooper said.

The SUV was traveling as fast as 50 mph (80 kph) when it crashed, Nueces County sheriff's Capt. Daniel Lorberau said. Several people had to be extricated and were taken to hospitals. In addition to the dead and critically injured, three others suffered lesser injuries.

Agents with the U.S. Border Patrol responded to the scene because the victims from El Salvador, Guatemala and Mexico entered the country illegally, authorities said. Authorities had previously said the victims were from El Salvador.

The incident is the latest involving undocumented migrants who died in road wrecks while being smuggled through Texas. This kind of multi-fatality traffic crash has become more common along the U.S. 77 corridor through South Texas because of its proximity to the U.S.-Mexico border, Hooper said.

"It has a classic appearance of human trafficking," he said. "We are a pipeline. We are on a corridor to Houston, Texas, and these first responders deal with it every day."

Five people died last June about 100 miles (161 kilometers) southwest of San Antonio when an SUV carrying 14 people crashed while being chased by Border Patrol and other law enforcement agencies.

In 2015, six of 14 people packed into an SUV were killed when their vehicle wrecked as police gave chase about 90 miles (145 kilometers) southwest of Houston.

Fifteen people died in 2012 when their pickup veered off a highway southeast of San Antonio.

Several other crashes have occurred in recent years involving fewer victims.