It was unclear if more people were still trapped in the rubble. Mexican authorities had received no reports of missing people, but were exploring the wreckage with care in case survivors remained.
Emergency workers from the McAllen, Texas, Fire Department were helping in the search using rescue dogs and thermal imaging equipment to search for survivors.
Mexican authorities said a gas leak Saturday triggered an explosion at about 8:30 a.m. that leveled a two-story cement building containing a restaurant and clothing stores. The blast also flattened a neighboring three-level shopping center where a dentist office, pharmacy and souvenir shops were located.
Six people were killed by the explosion, and 14 remained hospitalized - three in critical condition, said Raul Herrera, a Nuevo Progreso police officer.
Witnesses said the ground shook and a thick cloud of dust filled the air in the shopping district located about two blocks from the international bridge over the Rio Grande that connects Mexico and the United States.
Jacobo Gaytan, 27, had just finished mopping the floor in front of his candy stand in the entrance to the shopping center when he heard a loud thud and felt a gust of wind lift him from the ground.
``When I got up, I was bleeding and had pieces of glass all over my body,'' Gaytan said. His whose face and arms were covered with cuts.
Investigators said the blast, which shattered windows up and down the street, appeared to be accidental.
``It's known it was a gas leak, but whether it came from the restaurant or the dentist office is still under investigation,'' said Jose Cerecedo, director of public safety for Nuevo Progreso.
The town of 15,000 across the U.S. border from Progreso, Texas, is a popular tourist destination. The affected businesses were closed but employees were in the buildings cleaning and preparing to open, Cerecedo said.
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