Hong Kong lawmakers urged calm Tuesday after police arrested 10 people on suspicion of making explosives in a plot they say is linked to a "radical" group, ahead of a vote on a controversial political reform package.

The allegations have been met with scepticism from security experts and commentators in the southern Chinese city, who questioned its timing ahead of the vote, expected Friday.

Police said one of the ten suspects had claimed to be a member of a "radical local group", but would not name the group or specify motives.

They said maps of central Hong Kong districts had been found and warned anyone taking part in public gatherings to stay away from "violent protesters".

Daily rallies are being held at the city's legislature ahead of the vote by lawmakers on the government's controversial political reform package.

All 10 suspects were arrested Monday "on suspicion of conspiracy to manufacture explosives" and detained overnight. The tenth, a 58-year-old man, was taken into custody at the northern border point of Lo Wu late Monday.

Police also seized chemicals at an abandoned television studio in the eastern district of Sai Kung Monday, with some detonated at the scene.

A later house search led to the seizure of ingredients which police said could be used to make TATP, a highly-volatile explosive believed to have been used in the deadly terror attacks in London in 2005.

Air rifles and "V for Vendetta" style face masks were also found.

"I suggest we look very carefully, deeply and calmly at this case before we give this individual incident too much priority," security expert Steve Vickers told AFP.

"The timing is obviously of considerable interest."

Vickers said it was easy to find the ingredients for TATP online -- but would be difficult to manufacture the explosive itself.

"The persons who are accused of possessing this, unless they are experts, probably present a greater threat to themselves than the public if they try and transport this material," said Vickers, a risk consultant and former head of the Royal Hong Kong Police's Criminal Intelligence Bureau.

Local media named the radical group as the National Independent Party and linked it to a new "localist" pro-democracy movement which is seeking a more independent Hong Kong.

A Facebook page purportedly for the group, which only had posts from within the last 24 hours, showed an image of the Statue of Liberty carrying a sickle.

A previous page for the group, created in January, was taken down Monday.

Local media quoted the old page as saying: "Hongkongers must be prepared that there would be casualties," on the June 17, the day the reform bill goes to the legislature for debate.

But there was further scepticism among pro-democracy and localist campaigners.

"People have never heard of the organisation and don't know its members. The whole thing could be a set-up intended as a smear campaign against the localist camp," said political commentator Kam Sai-kit, writing for pro-democracy portal Post852.

Lawmaker Emily Lau, chairwoman of the Democratic Party, urged calm.

"I always call on the people not to resort to force and violence, because you will be met with even more force and violence," Lau told AFP.

"Hong Kong is world famous for being civilised and restrained... I hope we will stay that way."

The reform bill lays out a proposal for the public to choose the city's next leader for the first time in 2017.

But it sticks to a ruling from Beijing which stipulates candidates must be vetted by a loyalist committee.

That ruling sparked mass rallies and roadblocks towards the end of last year, with campaigners dismissing it as "fake democracy".

Pro-democracy legislators are vowing to block the proposal.