At least 21 people were killed as anti-China riots in southern Vietnam escalated and spread to the center of the country on Thursday.

A doctor in Ha Tinh province described five of the dead as Vietnamese workers and others as Chinese. He said they were among roughly 100 people sent to his hospital, Reuters reports. Over 600 Chinese have fled across the border to Cambodia.

The riots erupted following a large-scale demonstration on Tuesday to protest China’s May 1 deployment of an oil rig in waters claimed by both Beijing and Hanoi, triggering the most critical stand-off between the two countries in over three decades.

Read more: http://time.com/100492/vietnam-anti-china-riots-21-dead/