A former Catholic bishop of Hong Kong has warned of China's growing influence and urged Christians to unite in the "fight" for democracy.

Cardinal Joseph Zen Ze-kiun, who at 82 is one of the oldest campaigners to have joined the Occupy Central movement for democracy in the recent mobile-phone torchlit protests in the streets, warned that China's influence is increasing "day by day". He said Christians must be prepared to battle for their beliefs if religious freedom in the former British territory is not to become a thing of the past.

The cardinal, who served as bishop between 2002 and 2009 and has been active in the pro-democracy movement for decades, said: "Beijing are taking more and more control of Hong Kong, and going back on the promises of the constitution.

"All of these efforts, all of this courage to take risks and be ready to pay the price is because we are fighting for something very important. If [the Hong Kong leader is chosen by Beijing]...then he will surely do anything that the central authority commands."

The Cardinal added that "the Communist party have no interest other than their own power, and they made whole people into slaves."

The protestors are angry at the Chinese government's insistence on screening political candidates to ensure their allegiance to the CCP.

It was hoped that open elections would be held in 2017, but a motion ruling against this was passed in August. Many locals believe this to contradict Beijing's promise to one day allow Hong Kong "universal suffrage".

Cardinal Zen spent days addressing the crowds, many of them students, and spent nights sleeping on the streets in the hopes of making the voice of the people of Hong Kong heard.

"Beijing are taking more and more control of Hong Kong, and going back on the promises of the constitution," he told Christian Today.

"All of these efforts, all of this courage to take risks and be ready to pay the price is because we are fighting for something very important. If [the Hong Kong leader is chosen by Beijing]...then he will surely do anything that the central authority commands.

"And [the CCP] are also corrupt, not only in the sense of bribery, but they also corrupt the culture, the way of life – people become materialistic, selfish, dishonest and ready to accept slavery," he said.

"Everybody becomes desperate in their own field. This terrible culture is against what we have instilled here in Hong Kong in our education and in our schools. And in the long run, sooner or later – or very soon – we are going to become like in China, and that is terrible."

Cardinal Zen, who was Shanghai born but moved to Hong Kong ahead of the CCP's establishment in 1949, believes speaking out for democracy and freedom is a vital part of his Catholic faith, as well as his position in leadership.

"This is in the teaching of the church; the social teaching says that the participation of people is important," he said.

"Because we care for human dignity, we are children of God and we can't be made into slaves: that is the reason we must fight."

This week the Occupy Central movement has appeared to be on the wane, with just a few hundred protestors – most of them students – remaining, and leaders said last night that they had agreed to hold talks with the government.

Cardinal Zen called on those still demonstrating to go home, but not to give up.

"At this moment, the students should retreat, because to retreat doesn't mean to abandon the cause," he explained.

"We have made the point, and we may still make our demands but we must rest a little...There is no way to reason with people who are simply unreasonable; we have to gather and think about the next steps. I think at this moment, one important thing is that we must understand that this movement does not belong to the students anymore, and nor does it belong to the promoters of the Occupy Central movement, but it belongs to the whole people.

"There should be a wider consultation, a commission, and then our voice will be stronger and we can make plans," he said.

"For the moment, the battle is going to be long and we must be wise."

The Cardinal's main concern remains freedom of religion in Hong Kong, which hangs in the balance as Beijing makes its bid for power clear.

"At this moment, they have already taken away from the Church our right to run our schools. The next step maybe is to demand heavy taxes from churches, and then it will be the same as China. It is not at all impossible, and we are to fight now before it's too late," he said.

"It's very dangerous, every day Beijing increases its influence. It's already too late maybe, but at least now finally the people have awakened – the whole people are with us."