A software engineer claimed to have installed such systems in police stations in the province.

A human rights advocate who was shown the evidence described it as shocking.

The Chinese embassy in London has not responded directly to the claims but says political and social rights in all ethnic groups are guaranteed.

Xinjiang is home to 12 million ethnic minority Uyghurs, most of whom are Muslim.

Citizens in the province are under daily surveillance. The area is also home to highly controversial "re-education centres", called high security detention camps by human rights groups, where it is estimated that more than a million people have been held.

Beijing has always argued that surveillance is necessary in the region because it says separatists who want to set up their own state have killed hundreds of people in terror attacks.