By Francis Markus BBC correspondent in Shanghai

A landmark trial has begun in Hong Kong of 12 practitioners of the Chinese Falun Gong spiritual movement.

They are accused of obstruction and assault against police during a protest outside Beijing's liaison office in the territory, to highlight cases of Falun Gong followers they say face imprisonment and sometimes death in mainland China.

This is the first criminal trial to have been launched in Hong Kong against practitioners of the spiritual movement.

It is regarded by local human rights activists as a test of the freedoms Beijing guaranteed to maintain in the former British colony after it was returned to China in 1997.

The activists say those freedoms are being steadily eroded. Falun Gong remains legal in Hong Kong even though it is outlawed by the authorities in the Chinese mainland.

China's fears

Beijing's Communist leaders regard the movement's grassroots following as a major threat to the party's social control.

And Falun Gong followers allege that hundreds of their number in China have died in police cells.

China is fearful of the group's influence

The 12 local residents and four Swiss nationals now on trial in Hong Kong face charges of obstruction in a public place, stemming from a protest in March outside Beijing's liaison office in the territory.

Some of them also face more serious charges of obstruction and assaulting police.

A Falun Gong spokesperson outside the courtroom told the BBC that the movement had confidence in the territory's legal system, despite heavy political pressure from Beijing.

But if the practitioners are found guilty in the trial - expected to last several days - they could face jail terms ranging from three months to two years.