At least 31 people are dead and more than 50 missing after flash floods hit a town in northern Mexico, close to the US border.
The devastation was "enormous", the governor said.
Heavy rain caused a local river to burst its banks, inundating the area.
The flood waters swept through the town of Piedras Negras in the state of Coahuila, across the border from Eagle Pass in Texas.
Thousands are homeless. Buildings have been damaged, power lines brought down and cars overturned.
Two of those killed were
children, and more than half were elderly, according to rescue workers.
Coahuila's governor said the flooding had been among the worst-ever in the
region, adding that "the magnitude of destruction is enormous".
Pounding rain hit the town at dawn, forcing the Escondido River, a tributary of the Rio Grande, to rise by nearly eight metres (25 feet).
It was the first recorded time the river had burst its banks, officials said.
Braced for more
One of the worst hit districts was the Villa de Fuente neighbourhood, where hundreds of homes were flooded.
A bridge linking the town across the border to Texas was damaged.
Emergency workers have evacuated residents from low-lying areas to shelters in case of more flooding.
About 3,500 people have been made homeless
"There are warnings that another wave of water could arrive. We're calling on people not to return to their houses," the town's Red Cross chief, Alfonso Bres, told AP.
Later on Monday floodwaters receded, allowing President Vicente Fox to visit the area.
"We will help each and every one of you recover your
homes, furniture, belongings," he said.