The six included prominent young campaigner Nathan Law, 27, who recently relocated to Britain after fleeing Hong Kong.
“Hong Kong police officially ordered the arrests of six trouble-makers who have fled overseas,” CCTV state television said.
Law called the charges “trumped-up” and said his only “crime” is that he “loves Hong Kong too much”.
“The arrests, the disqualifications, the wanted bulletins - these are indications of our need to remain active on the global stage,” Law said on Facebook.
“That Hong Kong has no place for even such moderate views like ours underscores the absurdity of Chinese Communist rule.
“I hope... that all of you can stand strong to resist the white terror rather than succumb to self-censorship,” he added.
A crackdown on Hong Kong’s democracy movement has increased apace in the month since Beijing imposed a sweeping national security law on the restless city.
The law targets subversion, secession, terrorism and colluding with foreign forces with up to life in prison, but critics said it was a legal weapon to silence dissidents and criminalise certain political views.
It would be the first time the city’s police have used the extraterritorial power in the new law to go after activists who are not in the territory.
Besides Law, the other activists sought include former British consulate staffer Simon Cheng, pro-democracy campaigner Samuel Chu and pro-independence activists Ray Wong, Wayne Chan and Honcques Laus, according to CCTV.
“Hong Kong police is targeting a US citizen for lobbying my own government. I might be the first non-Chinese citizen to be targeted, but I will not be the last,” Chu said on Twitter.
“If I am targeted, any American, any citizen of any nation who speaks out for HK can-and will be-too,” he added.
The report said the six were sought for “incitement to secession and collusion with foreign forces”.
However, in an email to AFP, the Hong Kong police said they ‘do not comment on media reports”.
Beijing has said the law will restore stability after last year’s huge and often violent pro-democracy protests.
But it has also hastened the unravelling of Hong Kong’s political freedoms and autonomy, supposedly guaranteed for 50 years after the 1997 handover from Britain.
In just a month since the new security law came into effect, a dozen leading pro-democracy campaigners have been disqualified from running in legislative elections and four students have been arrested on suspicion of “inciting succession” with social media posts.