A man clearing barricades in Hong Kong was hit in the head with a street drain cover over the weekend, marking a violent return to anti-Government demonstrations across the Asian financial hub.

Key points: Police condemned the unprovoked attack and have classified it as assault

Police condemned the unprovoked attack and have classified it as assault Anti-Government protests returned to the city after a relative lull in demonstrations

Anti-Government protests returned to the city after a relative lull in demonstrations UN rights chief Michele Bachelet has called for an independent investigation into HK police

The man was struck in the head with a drain cover by a masked assailant in the early hours of Sunday morning.

Video posted online shows the man standing among a crowd of black-clad men attempting to record a scene with his phone when the assailant runs up and strikes him.

Police have "seriously condemned" the brazen attack, which has been classified as an assault.

In the largest of the three protests, a key thoroughfare along the waterfront on the Kowloon side of Victoria Harbour was packed with demonstrators ranging from hardened masked protesters in all-black outfits to families and the elderly.

Protesters have returned to Hong Kong's streets following a lull in activity during local district council elections. ( AP: Vincent Thian )

They chanted "five demands, not one less" and "disband the police force" as they marched, in reference to the protest movement's five formal demands of the Government.

So far, only one has been met — the formal removal of a extradition bill that would have allowed people within Hong Kong to be arrested and tried in mainland Chinese courts.

The remaining demands include granting Hongkongers universal suffrage, the release of all imprisoned protesters, the de-classification of a June protest as a "riot", and the formation of an independent commission of inquiry into police behaviour.

That rally followed two other marches earlier Sunday as protesters sought to keep the pressure on city leader Carrie Lam after the recent win by the pro-democracy camp in district council elections and the gaining of US support for their cause.

"If we don't walk out, the Government will say it's just a youth issue, but this is a Hong Kong problem that affects all of us," said Lily Chau, 30, as she pushed her toddler in a stroller at the march in Kowloon.

"If we are scared, the Government will continue to trample on our rights."

Thousands of protesters returned to Hong Kong's waterfront over the weekend. ( Reuters: Leah Mills )

Police estimated that 16,000 people attended the Kowloon rally.

Slogans spray-painted along walls and on sidewalks reminded the crowd that "freedom is not free" and pledged "victory at all costs."

The Kowloon march was cut short after riot police fired tear gas and arrested a few people.

A police statement said minimum force was deployed after "hundreds of rioters hurled smoke bombs" and bricks.

'Are you trying to kill us?'

Anti-Government protesters have called for an independent inquiry into alleged instances of police brutality. ( AP: Ng Han Guan )

Marchers berated police as they scrambled to flee the tear gas, shouting "dirty cops" and "are you trying to kill us?"

Some protesters dug up paving stones and threw them on the street to try and slow the police down.

More tear gas was fired at night after dozens of hardcore protesters set up roadblocks and vandalised some shops and restaurants linked to China.

Hong Kong's protests have been relatively peaceful during the two weeks around the November 24 elections, but Sunday's disruption indicated there might be more violence if Ms Lam failed to yield to protesters' demands.

Hundreds of elderly Hongkongers marched with protesters on Saturday. ( AP: Ng Han Guan )

Ms Lam has said she will accelerate dialogue but has refused to offer any new concessions since the elections.

Her Government has accepted only one demand — withdrawing extradition legislation that would have sent suspects to mainland China for trial.

Elaine Wong, an office worker who was at the Kowloon march, called the recent election win "an empty victory".

"We have in actual fact not won any concessions for our demands," she said.

"We must continue to stand out to remind the Government of our unhappiness."

UN rights chief calls for investigation into HK police

Protesters have called on the Trump Administration to do more to assist their calls for democracy. ( AP: Ng Han Guan )

The two earlier marches Sunday appealed to US President Donald Trump for help and demanded that police stop using tear gas.

Waving American flags, black-clad protesters marched to the US consulate to thank Mr Trump for signing into law last week legislation supporting their cause and urged him to swiftly sanction Ms Lam and other officials for suppressing human rights.

Some held banners reading, "Let's make Hong Kong great again" — a riff on Trump's 2016 campaign pledge to "make America great again".

One showed him standing atop a tank with "Trump" emblazoned on the front and side.

At the other small rally, a peaceful crowd of about 200 adults and young children marched to Government headquarters in the morning and chanted, "No more tear gas".

"A lot of parents are worried that their children are affected, because their children are coughing, breaking out in rashes and so forth," said social worker and march organiser Leo Kong.

There have been numerous instances where bystanders have been caught up in tear gas clouds in Hong Kong. ( AP: Vincent Yu )

In Geneva, China accused the UN high commissioner for human rights, Michelle Bachelet, of emboldening "radical violence" in Hong Kong.

In an opinion piece published Saturday in Hong Kong's South China Morning Post newspaper, Ms Bachelet called for an "independent and impartial judge-led investigation into reports of excessive use of force by the police."

She also said that Ms Lam's Government must prioritise "meaningful, inclusive" dialogue to resolve the crisis.

China's UN mission in Geneva said the article interfered in China's internal affairs and exerted pressure on Hong Kong's Government and police, which "will only embolden the rioters to conduct more severe radical violence".

It said Ms Bachelet made "inappropriate comments" on Hong Kong's crisis and that the Chinese side had lodged a strong protest in response.

ABC/Reuters