A government ban on demonstrators wearing face masks, aimed at helping to quell months of pro-democracy unrest in Hong Kong, is unconstitutional, the territory's high court ruled on Monday.

"The restrictions it imposes on fundamental rights [...] go further than is reasonably necessary [...] and therefore fail to meet the proportionality test," the court said, according to a press summary.

The ban on face-covering came into force in October, when the city's unelected pro-Beijing leader invoked colonial-era legislation for the first time in more than 50 years.

The move was seen as a watershed legal moment for the city since its 1997 return by Britain to China — but has been largely symbolic.

Demonstrators — most of them wearing masks — have continued to clash with police, often violently, as they press their demands for greater democracy for Hong Kong, as well as an independent inquiry into alleged brutality by the increasingly unpopular police force.

Meanwhile, Hong Kong police fought off protesters with tear gas and batons on Monday as they tried to break through a police cordon that is trapping hundreds of them on a university campus.

Protesters advanced on the police from outside the cordon, while others emerged from the campus, their trademark umbrellas at the fore. Police used tear gas and in some places swooped in to subdue protesters and make arrests. It wasn't clear if any of those inside Hong Kong Polytechnic University escaped.