HONG KONG -- Police repeatedly fired tear gas and rubber bullets to drive back protesters blocking Hong Kong streets with road signs and umbrellas Sunday in another night of pitched battles as protests for democracy in the Chinese territory escalate.

It was the second night in a row that tear gas was used against protesters. Their demonstrations began early last month in opposition to an extradition bill that has since been suspended, but the movement has become a broader push for full democracy.

Protesters occupied two areas at opposite ends of central Hong Kong on Sunday following a midafternoon rally against police use of tear gas at a demonstration the previous weekend.

On the western end of Hong Kong Island, one group blocked areas near the Chinese government's liaison office and began to move forward as night fell. Police issued warnings, and protesters threw eggs at them. Officers fired tear gas to halt the advance.

Police then embarked on an hourslong effort to push the protesters eastward and get them to disperse.

In repeated standoffs, spontaneous but highly organized protesters set up behind scaffolding that they built across a street. Police lined up behind clear shields about 30 metres (100 feet) down the road. Dozens of journalists in bright yellow vests stood on the sidelines between the groups.

The police would advance gradually, firing bursts of tear gas. Protesters in hard hats scurried about, rearranging makeshift barriers of pilfered road signs and other items. By the time the police reached the scaffolding, they had backed off about 6 metres (20 feet).

Another team of officers, more mobile with smaller shields, then swept in to clear the area. Local media reported some protesters were detained.

For more than seven weeks, protesters have taken to Hong Kong streets, initially to demand the scrapping of a proposed extradition law that would send suspects to mainland China to face trials. The legislation is seen as a threat to Hong Kong's freedoms that were guaranteed for 50 years when China took back control of the former British colony in 1997.

The bill was eventually suspended, but the protesters then called for the resignation of the city's leader and an investigation into whether police have used excessive force in quelling the protests.

Underlying the movement is a push for full democracy in the city, whose leader is chosen by a committee dominated by a pro-Beijing establishment, rather than by direct elections.

Earlier Sunday, protesters rallied at a park in Hong Kong's financial district before marching out in several directions despite not winning police approval for a public procession. It was the second straight day that protesters took to the streets without official permission.

A sea of black-shirted protesters, some with bright yellow helmets and masks but many with just backpacks, streamed out of Chater Garden park. Chanting "Add oil," a phrase that roughly means "Keep up the fight," a huge crowd marched east down a wide thoroughfare.

They stopped near the Sogo department store and set up barricades to block off the area and defend it against police.

Another group headed west toward mainland China's liaison office. Protesters egged the office last weekend and splattered black ink on the national emblem, eliciting an angry reaction from the Chinese government.

Some stopped about two blocks short of the office and used orange and white construction barricades to build a wall spanning a major road. They massed behind the barriers as night fell, with umbrellas pointed forward to shield their identities and ward off any police move to clear them.

Some nearby stores shuttered early as police in riot gear gathered nearby ahead of the all but inevitable clearing operation.

The rally in Chater Garden was called to protest the police use of tear gas, rubber bullets and other force to break up a protest the previous Sunday.

"We need to have a protest to show that we are strongly against this kind of brutality and we need them to respond to our demands," said rally organizer Ventus Lau.

Police had denied Lau's request to march west to the Sheung Wan district, where the tear gas was used the previous weekend, citing escalating violence in clashes with protesters that have broken out after past marches and rallies.

"The police must prevent aggressive protesters from exploiting a peaceful procession to cause troubles and violent clashes," said Superintendent Louis Lau of the police public relations branch.

On Saturday, police fired tear gas and rubber bullets as demonstrators threw bricks and other objects and ducked behind makeshift shields at a march in an outlying district toward the border with mainland China.

Police had also denied permission for that protest in Yuen Long, where a mob apparently targeting demonstrators had beaten people brutally in a train station the previous weekend.

Police wearing helmets charged into the same train station, where a few hundred protesters had taken refuge from the tear gas. Some officers swung their batons at demonstrators, while others appeared to be urging their colleagues to hang back. For the second week in a row, blood was splattered on the station floor.

Police arrested 13 people, including march organizer Max Chung, for offences including unlawful assembly, possession of offensive weapon and assault, according to police and Hong Kong media. At least four officers were injured.

The Hospital Authority said 24 people were taken to five hospitals. As of Sunday morning, eight remained hospitalized, two in serious condition.

Amnesty International, the human rights group, called the police response heavy-handed and unacceptable.

"While police must be able to defend themselves, there were repeated instances today where police officers were the aggressors," Man-kei Tam, the director of Amnesty International Hong Kong, said in a statement.

Police said they had to use what they termed "appropriate force" because of the bricks and other objects thrown at them, including glass bottles with a suspected corrosive fluid inside.

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Associated Press writer Ken Moritsugu in Beijing contributed to this report.