Thousands of pro-democracy campaigners remain on the streets of Hong Kong, demanding the right to choose their next leader.

There has been no repeat of the tear gas used to disperse protests over the weekend, but China has warned other countries not to interfere in the affairs of the former British colony.

There is concern among protesters that police may try to clear the streets ahead of Chinese National Day tomorrow.

Demonstrators have set a deadline of Wednesday for the government to respond to demands for reforms, as protests enter a fifth day.

In his first public comments since police fired tear gas at demonstrators, Hong Kong's chief executive Leung Chun-Ying called on protest leaders to "immediately" withdraw their followers from the streets.

"Occupy Central founders had said repeatedly that if the movement is getting out of control, they would call for it to stop," he said. "I'm now asking them to fulfil the promise they made to society, and stop this campaign immediately."

Umbrella revolution

Occupy, the main group behind the last two days of street protests, rejected Mr Leung's demands and renewed its calls for him to step down.

"If Leung Chun-Ying announces his resignation, this occupation will be at least temporarily stopped in a short period of time, and we will decide on the next move," co-founder Chan Kin-Man told reporters. "This would be a very important signal, then at least we know the government has changed their attitude and wants to solve this crisis."

Some demonstrators have worn masks and resorted to umbrellas or plastic capes to protect themselves - prompting the phrase "umbrella revolution" to trend on social media.

However, in a shift of tactics, uniformed police looked on from behind barricades and have so far not intervened in the peaceful protest.

On Sunday night, riot officers fired 87 rounds of tear gas after being charged by "violent protesters", with police saying 41 people had been injured.

The UK Foreign Office said it was "concerned" by the heavy response in its former colony - but China has warned the international community not to "interfere".

Officials called on the activists to leave peacefully on Monday but thousands remained camped on a normally busy road near government headquarters.

Organisers estimate as many as 80,000 people have taken to the streets since Friday.

Social media

With no imminent end in sight, China appears to have blocked photo-sharing site Instagram, suggesting authorities are worried about inspiring similar protests on the mainland.

Many shared photos of the demo have been hashtagged "Occupy Central".

The phrase was also blocked on Sunday on Weibo, China's version of Twitter.

The unrest began after it was ruled that in 2017 Hong Kong residents must choose their leader, or chief executive, from candidates picked by Beijing who must declare their "love" for China and its Communist system.

Under the agreement of the 1997 handover from Britain to China, Hong Kong was given an independent legal and political framework.

Unlike the mainland, protests are allowed - but the current demonstrations are potentially the biggest political challenge to Beijing since the Tiananmen Square crackdown 25 years ago.

The protests have affected Hong Kong's important commercial hub, forcing buses to be cancelled or diverted and some banks to close.