UPDATE 2-Magnitude 5.5 quake jolts central Chile, no damage

* Buildings sway in capital Santiago

* No reports of injuries, damage-emergency office

* Codelco, Anglo American mines operating normally

SANTIAGO, Oct 11 (Reuters) - A moderate earthquake struck Chile's central region on Thursday afternoon, causing buildings to sway in capital Santiago though there were no reports of injuries, damage to infrastructure or disruptions in the country's massive copper mines.

The tremor hit 43 miles (69 km) northeast of Santiago at a depth of 50.9 miles (81.9 km), according to the U.S. Geological Survey, which downgraded the quake to magnitude 5.5 from an originally reported 5.7.

World No. 1 copper producer Codelco said its nearby mines were operating normally after the quake, as was global miner Anglo American Plc's south-central Los Bronces copper deposit, a union leader told Reuters.

"Everything is calm. Everything is operating normally," Jose Navarro, a union leader at Los Bronces told Reuters.

Seismically-active Chile was battered in February 2010 by an 8.8 magnitude quake and ensuing tsunami, which caused billions in damage and killed hundreds.

In Thursday's quake there were no reports of injuries, disruptions to basic services or infrastructure damage, the country's emergency office Onemi said.

Cell phone lines, however, appeared to be down and alarmed shoppers left malls following the tremor, according to local radio. Following a strong quake, cell phone lines typically clog up as concerned residents call relatives and friends.

The quake did not meet the conditions needed to trigger a tsunami, Chile's navy said.