TIJUANA, Mexico -- A moderate earthquake struck northwestern Mexico near the U.S. border Monday, prompting authorities to evacuate schools and resulting in at least one minor gas leak.

No major damage or injuries were reported from the temblor, which an expert said was likely an aftershock from a magnitude-5.4 quake three days earlier.

The magnitude-4.9 quake hit around 10:30 a.m. PST. It was centered about 20 miles southeast of the border city of Mexicali, and 24 miles southeast of the U.S. border city of Calexico, Calif., according to the U.S. Geological Survey. The magnitude was revised downward from an initial calculation of 5.1.

In Mexicali, an industrial city of about 750,000, the quake caused the wall of a school to fall and started a gas leak in a second school, prompting authorities to evacuate all of the city's learning centers, said Alfredo Escobedo, civil protection director for the Mexican state of Baja California.

Escobedo said no injuries or other damages had been reported.

The latest earthquake came three days after the Mexicali area was rocked by a magnitude-5.4 quake that shut down factories and left 400,000 people without power.

There were no reports of immediate damage or injuries on the U.S. side after the Monday morning quake, according to the Imperial County Sheriff's Department and Calexico police.

The quake was felt in parts of San Diego, Imperial and Orange counties and as far away as Yuma, Ariz., according to the USGS.

The latest temblor was likely an aftershock, said Julie Martinez, a geophysicist at the National Earthquake Information Center in Golden, Colo.

A series of smaller quakes, ranging from magnitudes 2.5 to 2.9, preceded Monday's temblor and there were at least five aftershocks, including one registering a magnitude-3.6, the USGS said.

In 2000, the northern Baja California region near Mexicali was rattled by a cluster of quakes, but it did not cause any apparent damage.

"It's a seismically active region," Martinez said. "We haven't had a series like this in a while. It's definitely not unusual."