MEXICO CITY (AP) — A moderate earthquake rocked Baja California, shutting down factories near the U.S. border and leaving 400,000 people without power into early Saturday, authorities said.

However, no major damage or injuries were reported.

The quake that struck at about 11:12 p.m. Friday had a magnitude of 5.1, according to the U.S. Geological Survey in Golden, Colo. It had initially calculated the magnitude at 5.4.

The quake was centered 20 miles southeast of the border city of Mexicali and about 100 miles east of Tijuana.

"It has been felt pretty widely in Southern California, southwestern Arizona and probably northern Mexico," said USGS geophysicist Jessica Sigala.

It was followed by at least 25 smaller aftershocks.

The quake left about 400,000 people without electricity and 1.2 million without cellular telephone service, but service was restored at around 4 a.m. local time, said Fire Capt. Rene Rosado, director of civil defense in Mexicali.

About 80,000 workers were evacuated from or were unable to enter local factories for Sony, Honeywell and other major corporations, he said, but the factories had all reopened by Saturday afternoon.

Two bridges showed 2-inch to 3-inch cracks and were closed until engineers could determine they were safe, he said.

Rescue workers were examining Mexicali schools, many of which are made of adobe, for cracks and other damage, said Alfredo Escobedo, director of Baja California civil protection.

Oscar Vega, the state's education secretary, said classes were expected to resume Monday, but his department would make an announcement when it knows if the buildings are safe.

A magnitude-5.4 temblor struck the Mexicali area in 2006, but there were no injuries or damage.