Zhang Yadi, 22, was arrested on July 31 in the southwest province of Yunnan and was being held in her hometown in central Hunan province, New York-based Human Rights Watch said in a statement released Tuesday.

The rights group believes she was detained for undermining "national unity," a charge that carries a prison sentence of up to 15 years under Chinese law.

Zhang was the editor of a Chinese-language digital platform whose stated objective was to "promote Tibetan culture, ease ethnic tensions, and encourage transitional justice and reconciliation", according to her X account.

She had studied at the Ecole Superieure de Commerce de Paris (ESCP) and was due to continue her studies in London in September, according to the Human Rights Watch statement.

"The history of China's southwestern ethnic groups is a bloody tale of Han Chinese colonising, enslaving, and assimilating the indigenous peoples," Zhang had posted on X.

The Han are the majority ethnic group in China, making up more than 90 percent of the population.

Human rights organisations accuse China of repressing religious freedom in Tibet and imposing strict surveillance of the population.

For its part, Beijing claims to have drastically improved living conditions for the inhabitants.