BEIJING -- A strong aftershock on Tuesday rocked the southwest Chinese province struggling to recover from a devastating earthquake, sparking fear among office workers who ran onto the street, state media said.

The tremor, measuring 6.1 on the Richter scale, shook Chengdu, the capital of Sichuan province, at around 3:10 pm (0710 GMT), the Xinhua news agency said. The US Geological Survey measured the aftershock at magnitude 5.9.

Workers rushed from their buildings after the "strongest aftershock" since a 7.9-magnitude quake hit Monday, leaving tens of thousands of people dead or missing in and around Sichuan.

The region has been pummeled by wave after wave of terrifying aftershocks up to magnitude six, hampering rescue efforts, the Sichuan provincial seismological bureau said earlier.