A small earthquake rattled Littleton and at least 12 other cities and towns early this morning but caused no damage, according to police and a seismologist. The epicenter of the 2.5 magnitude tremor struck near Littleton Common at 1:23 a.m. and woke up most of town.

"We had so many 911 calls they were going to our backup, which is Ayer," said Sergeant Robert Romilly of the Littleton Police Department. "We had two people working the phones, and we still couldn't keep up. It was just one after the other after the other."

The quake appears to have been followed by a 0.9 magnitude aftershock at 6:04 a.m. and several other smaller rumbles, said John Ebel, the director of Weston Observatory at Boston College. Ebel was still studying seismic charts to determine the number and size of the aftershocks.

People reported feeling the quake in Groton, Shirley, Boxborough, Ayer, Harvard, Townsend, Westford, Pepperell, Acton, and Fitchburg, according to the US Geological Survey's website. The area has experienced roughly a dozen small tremors since the 1970s, Ebel said.

In Littleton, the quake shook the walls of the police station. Then the switchboard lit up. Callers told dispatchers that it sounded like a plane crash or a building exploding or a major accident on Interstate 495.

Police cruisers canvassed the interstate and drove through town looking for a calamity or "a glow in the sky" from an explosion, Romilli said. Officers found nothing, then learned what it was.

"The earthquake was the lesser of two evils. There was no damage," Romilli said. "Actually, I live in town, and I slept right through it."