However, there are no reports of major damage or injuries.
The U.S. Geological Survey says the quake struck at about 11:12 Friday night and was centered 16 miles southeast of the border town of Mexicali.
It was followed by at least 15 aftershocks, including one with a preliminary magnitude of 3.8.
Mexicali's director of civil defense says the quake knocked out power to 400,000 people and cell phone service to 1.2 million.
Two bridges were closed for inspection and about 80,000 workers in border factories were evacuated or were unable to go to work until the buildings have been declared safe.
The Baja peninsula is a geologically active region. In 2006, a magnitude-5.4 temblor struck the Mexicali area but there were no injuries or damage.
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