By Jared Taylor and Jim Forsyth

PALMVIEW, Texas (Reuters) - Nine people, all believed to be illegal immigrants, were killed in a late-night accident in southern Texas, authorities said on Wednesday.

The crowded van was carrying 19 people when it rolled over on Tuesday night on U.S. Highway 83, which runs parallel to the Rio Grande River that forms the U.S.-Mexico border, said Chris Barrera, the police chief in Palmview, Texas.

Barrera said that in addition to the nine people killed in the crash, six were injured. Three people fled the crash and two of them were later caught. He said all of the dead were believed to be in the United States illegally.

Barrera said the cause of the crash was not yet known. The van's driver had not been apprehended by late Wednesday afternoon, he said.

The rollover occurred after U.S. Border Patrol agents stopped the vehicle along a residential street near the highway, Barrera said. One person ran from the van during the stop before its driver fled the scene and turned onto a highway frontage road.

Border Patrol agents found the van after it had crashed into trash cans and a business sign, rolling over several times, Barrera said. The van's sliding door detached, tossing many of its passengers from the vehicle, he said.

Dianna Castillo, 23, stood in front of her home near the wreck on Wednesday morning.

"The bodies were everywhere," Castillo said. "I wanted to cry because it's really sad because they came over here to live a better life and then they lost their lives."

Lenny Sanchez, a Palmview police commander, said the wreck may have been caused by overcrowding in the van, which was designed for seven passengers. The van was missing its rear seats and had wooden blocks supporting its rear axle to allow more human cargo inside.

"We see this very frequently, of course," Sanchez said. "We often see vehicles filled with people and the driver takes off running or refuses to stop for police officers."

Coyotes, as human smugglers are known, often overload vehicles with illegal immigrants to spirit them from border areas to inland cities where they move on to destinations throughout the United States. Frequently driven at high speed to outrun law enforcement, the vehicles are top heavy and roll easily.

The accident, which occurred about 240 miles south of San Antonio, was the second of its kind involving suspected illegal immigrants in as many days. Seven miles west of Tuesday's accident, another person was killed and 17 were hospitalized when a van carrying immigrants rolled over Monday in La Joya, Texas.

Immigration and Customs Enforcement is investigating the human smuggling operation suspected to be behind Tuesday's accident, Barrera said. Authorities have not identified all the victims or their nationalities.

(Editing by Paul Thomasch, Corrie MacLaggan and Eric Beech)