A Beijing law professor who has been an outspoken critic of China's ruling Communist Party and President Xi Jinping was taken away by authorities on Monday, several friends and colleagues told Reuters.

Xu Zhangrun, 57, a professor at the prestigious Tsinghua University, came to prominence in July 2018 for denouncing the removal of the two-term limit for China's leader, which allows Xi to remain in office beyond his current second term.