The cause of the enormous blast, which created chaos in one of the capital’s most heavily populated areas, was thought to be an accident.

© Fernando Llano/Associated Press

A small company in northern Mexico had faced steep competition from China in making straps, plugs, fasteners, grommets, zip ties and clamps. Now, U.S. tariffs have driven a spike in his business.

Relying on Asian suppliers is no longer a safe bet for many factories in Mexico. Companies are racing to change, and they are being encouraged by the government.