WAXAHACHIE - A sport utility vehicle plunged off an unfinished bridge in northern Mexico early Thursday morning, killing seven North Texans, including four young children.

Alejandra Hernandez — whose 5-year-old son was killed in the accident — said the Waxahachie residents were visiting relatives in the state of Chihuahua, Mexico, when the Chevy Tahoe fell nearly 20 feet, landing on its roof in the Conchos River.

DIARIO DE JUAREZ/AP

A view of an unfinished bridge in Ojinaga, Mexico. A sport utility vehicle carrying eight people from Texas plunged off this bridge into a river before dawn Thursday, killing three adults and four children.

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“There were no signs or lights, nothing,” she said, arms crossed, tears leaking down her cheeks. “They fell in because it was dark.”

Family members believe part of the bridge was washed away during flooding in mid-September.

Eduardo Esparza, a government spokesman, said there were no signs or barriers keeping traffic off the bridge, which was on a dirt road near the border town of Ojinaga.

Mrs. Hernandez’s son, David, was one of three children buckled into the back seat of the champagne-colored Chevy Tahoe. He sat next to two 7-year-old girls, Daniella Rey and her cousin, Kaylinn Ortiz, who also died.

Carlos Rey Madrid, 36, his wife, Olga, 27; his mother, Margarita Madrid Gonzalez, and 2-year-old Gael Rey, also perished. The only survivor was Mrs. Rey’s mother.

Relatives in a second car driven by Ubaldo Ortiz were able to stop before reaching the edge of the bridge.

“It was like 2 in the morning, and we were just arriving at El Mezquite,” Mr. Ortiz told Mexican officials. “But we fell behind and, when we caught up, we saw the Suburban with its tires in the air.”

He said the seven died because they couldn’t be freed from their seat belts in time. Kaylinn was Mr. Ortiz’s daughter.

At the Reys’ residence in Waxahachie, relatives gathered in the family’s home next to a Christmas tree trimmed in red and gold. A white envelope was wedged in the branches. It was addressed in neat looping letters — “Daniella: To: Santa.”

Family members huddled before an end table with family photos and five burning candles. A flower vase was stuffed with $20, $50 and $100 bills, gifts from friends and relatives to defer the funeral bill that family members said would exceed $20,000.

A woman cradled a cell phone, speaking through sobs. Family members said she was speaking to her mother — the lone survivor of the crash — on the way back to Texas from Mexico.

“Try to calm down and sleep if you can,” she said. “We’re waiting for you.”

A family friend, Neomi Machuca, said the extended Rey family lived in a collection of three small homes clustered along a rural road. They barbecued on the weekends and played soccer in the yard.

“This isn’t the first time this kind of thing has happened when people go back” to Mexico, she explained. “Sometimes the road will just end — no lights, no blinkers, nothing. It’s dangerous.”

The Associated Press contributed to this report.