Beanbag rounds have been fired at protesters, according to news site South China Morning Post. According to the Post, they are small fabric shells that cause muscle spasms or temporarily immobilise targets.

In the past 20 minutes, the protest has taken a more serious turn as protesters tried to storm the LegCo complex and police responded with force, deploying tear gas and water cannon. It has led some analysts to speculate that the police might try and clear the scene tonight, but the crowds remain sizeable. For now, police appear to have withdrawn into the LegCo compound but they will be weighing up their options very seriously.

Demonstrators have thrown "debris and bricks" at police officers, according to a statement by Hong Kong Police Force on Twitter, confirming earlier reports.

Police repeat that they will use "appropriate force" if protesters do not back down.

Screen shots circulating on social media from local news outlets show huge plumes of what appears to be tear gas released on the streets of Hong Kong:

Protesters hit by tear gas are being treated by those on scene, according to the BBC's Pody Lui.

Image source, Pody Lui

Multiple witnesses have reported tear gas canisters being fired by police. Protesters were forced to retreat, tweets freelance journalist Timothy McLaughlin.

RTHK are reporting that police have fired tear gas at protesters, an escalation in the violence.

Tear gas was used in Tim Wah and Harcourt junction, local media said.

Hong Kong's Commissioner of Police, Stephen Lo, will hold a press conference at the police headquarters at 16:15 local time (08:15 GMT)

There are many parallels emerging between the anti-extradition protests happening today and what happened in 2014 when pro-democracy protesters occupied parts of central Hong Kong. Not least, it was raining!

Here is the story of how the humble umbrella came to symbolise a movement.

Police have used pepper spray and batons to beat back umbrella-wielding protesters who tried to reach Hong Kong's parliament.

Clashes broke out shortly after 15:00 (07:00 GMT) -- the deadline protesters had given for the government to abandon a controversial bill that would allow extraditions to China.

Protesters using umbrellas as shields could be seen trying to get closer to riot police protecting the Legislative Council building, with projectiles thrown at officers who responded with pepper spray and baton charges.

Protesters have begun charging with their umbrellas towards police, according to Reuters.

First aiders at the scene are helping protesters, some of whom have been hit in the face by pepper spray, as the Hong Kong Free Press tweets:

Police turned water cannons on full blast as protesters struggled to protect themselves with umbrellas:

Image source, Reuters

BBC News Chinese reporter Martin Yip says TV channels are showing live footage of the clashes and protesters have begun throwing bricks at police.

It's a scene of chaos between police and protesters, as researcher Adam Ni tweets.

Protesters begin to storm Hong Kong’s Legislative Council Complex via its car drop-off entrance. Police have fought back with pepper spray and diluted tear spray.

Police have fired a diluted pepper spray solution at protesters who were holding up umbrellas on Tim Wa Avenue. The incident was broadcast live on HK television stations.

Former Hong Kong Chief Secretary Anson Chan has dismissed assurances given by current leader Carrie Lam that an extradition law - should it pass - would not be abused by China.

"We fear if she receives a request for extradition, she will find it very difficult to resist," Ms Chan told the BBC's Andrew Wood. "I think the greatest disappointment to Hong Kong people is her failure to stand on stand on [their] side."

Tens of thousands of people are blocking major roads in protest at a bill that would allow extraditions to mainland China.

Here's an explanation of why this bill is so controversial.

Protesters who had previously retreated from lines of police have now returned, journalist Karen Cheung tweets.