Torrential rains swelled a tributary of the Rio Grande by 25 feet early Monday, causing a flash flood that inundated a Mexican border city, killing at least 31 people and forcing hundreds more into shelters.  

Dozens more people were missing; the death toll was expected to rise. Mexico declared a state of emergency in the area.

Floodwaters from the Escondido River began receding after the rain stopped by midday, but heavy, dark clouds loomed over Piedras Negras, a city of 200,000 people about 150 miles southwest of San Antonio. Supplies of drinking water, electricity and gas were cut.

Hundreds of people were left homeless, radio stations reported, and announcers read the names of people staying at shelters to help families find missing relatives.

The heavy rains began Sunday and the downpours intensified around midnight, causing the river to overflow and flooding dozens of houses in a working-class area of tin-roof shacks within 15 minutes, city officials said.

"Houses were completely swept away. Cars flipped over, some on top of each other," said Marcela Aguirre, spokeswoman for the city in Coahuila State. "There is no power, no gas, no water."

At least 31 people were killed, said Coahuila State Civil Protection Authority official Fernando Horta. More than half were elderly and two were children, Piedras Negras Red Cross President Alfonso Bres said.

Sixty people were reported missing, Bres said.

"Several senior citizens basically did not have the strength to resist," he said.

State authorities estimated that floodwaters destroyed or severely damaged at least 500 homes and 300 cars.

Mexico's Interior Department declared a state of emergency in the area, a declaration that releases federal funds to help the city rebuild.

Local factories offered shelter to their workers, radio stations reported. The population of Piedras Negras has swelled in recent years as residents from Mexico's interior arrived looking for factory work.

About 5 inches of rain fell on Piedras Negras and the basin feeding the Escondido River on Sunday night alone.

Emergency workers patrolled the city, moving residents from low-lying neighborhoods to shelters. Some evacuees were treated for hypothermia and the Red Cross was seeking donations of dry clothing and food.

"There are warnings that another wave of water could arrive," Bres said. "We're calling on the people to not return to their houses."

The US Border Patrol sent two helicopters to help locate survivors stranded on rooftops and clinging to tree branches. Mexican government helicopters arrived later from the Coahuila State capital of Saltillo.

A power blackout and overcast skies made it difficult to find people before dawn without help from the helicopters.

"There wasn't even moonlight," Bres said.

Piedras Negras Mayor Claudio Bres and Coahuila Gov. Enrique Martinez planned to tour the area later Monday.

Police assembled at the entrance to the city, trying to control the traffic that backed up for miles.

(China Daily April 6, 2004)