HONG KONG (AFP) - Hong Kong student pro-democracy leader Joshua Wong was released from custody just before midnight on Thursday (May 19), after being detained for running onto a motorway to intercept the motorcade of a top Chinese official.

The move came on the final day of a three-day trip by Mr Zhang Dejiang, who chairs China's communist-controlled legislature, for which frustrated protesters have been kept out of sight behind barricades in a security lockdown.

Mr Zhang's visit was the first by such a senior official for four years and comes as concerns grow that freedoms are under threat in semi-autonomous Hong Kong as Beijing tightens its grip.

Police chased a group of five protesters, including Wong, on Thursday as they ran along a major highway in eastern Hong Kong which had been cleared for Mr Zhang. They were carrying a sign calling for "self-determination".

The protesters were all members of Demosisto, a political party led by Wong, who became the face of major pro-democracy rallies in 2014.

They were detained before Mr Zhang's motorcade emerged from a tunnel.

"The five arrested persons were released on bail and will need to report back to police in mid-June," a police spokesman told AFP, adding that charges had not been laid.

They were arrested for "obstructing police officer in the execution of duty and disorderly conduct in a public place", she said.

Demosisto said Wong, who already faces two imminent verdicts and a possible prison sentence for protests in 2014, was released on a HK$500 (S$89) bail.

He has been in and out of court hearings for the past year after being charged with multiple offences linked to protests leading up to what became known as the "Umbrella Movement".

Wong faces charges of taking part in an unlawful assembly and inciting others to do so, which carry a jail term of up to five years.

The 19-year-old has always argued that the cases against him are political persecution.

Hong Kong is semi-autonomous after being returned to China by Britain in 1997, with much greater freedoms than seen on the mainland.

But there are fears those freedoms are being eroded by increasing interference from Beijing.