Hong Kong police have arrested four men whom they accuse of supporting people based overseas who "endanger national security".

The local arrests come two days after Hong Kong put up bounties for eight pro-democracy activists living abroad.

The bounties have sparked an overseas outcry and follow a sweeping national security law imposed by Beijing.

The four arrested include Ivan Lam, the former chair of disbanded political party Demosisto, local media said.

Demosisto was co-founded by activist Nathan Law, who now lives in the UK and is one of the targets of this week's bounty.

Earlier this week, Mr Law told the BBC that his life had immediately become more dangerous.

The eight subjects of the HK$1m (£100,581; $127,637) bounty are based in the UK, the US and Australia, countries that have no extradition treaty with China.

Hong Kong is a special administrative region of China. Under Beijing's "one country, two systems" policy, the people of Hong Kong enjoy wider freedoms compared to those living in the mainland.

However, pro-democracy protests in 2019 paved the way for the national security law, which came into force in June 2020. Police have since arrested 260 people for violating it.

The four men arrested Wednesday night are accused of "conspiracy to collude with a foreign country or with external elements to endanger national security" and "conspiracy to doing acts with seditious intent".

Their offences are punishable by life imprisonment under the national security law.

Also on Wednesday, police seized banners and flags of online shopping app Mee, that serves as a guide for Hong Kongers on restaurants, shops and service providers that support the pro-democracy movement.