Hong Kong Church leaders have condemned the violent assault on pro-democracy protesters and passengers at an MTR station in the city's Yuen Long area.

Footage shared on social media showed dozens of men wearing masks and white shirts attacking people inside the Yuen Long MTR station with rods and sticks. 

It came at the end of another march through the city against the extradition Bill, a hugely controversial piece of legislation that would allow some suspected criminals to be sent to mainland China for trial. 

The incident left 45 people injured, one person critically, and has shocked the city.

While there have been some clashes with police over the last seven weeks of protests, the Yuen Long attack reflects an alarming escalation of violence towards the protesters.

Protesters and lawmakers have accused the police of standing by while the men - believed by locals to be triad gangsters - launched their assault. 

The Catholic Diocese of Hong Kong has condemned the violence in a statement.

"We are greatly aggrieved by the outbreak of violent assault at our citizens at the Yuen Long MTR Station," it said. 

"We condemn violence of any nature and means, and earnestly hope that the offenders will be arrested and brought to justice. We also pray for the speedy recovery of the injured." 

Hundreds of thousands of people marched through Hong Kong on Sunday against the extradition legislation. 

Although Hong Kong chief executive Carrie Lam has said that the Bill is "dead", Hong Kongers have vowed to continue marching until it is fully withdrawn.

Ahead of Sunday's march, Su Chengyi, chairman of the Hong Kong Council of Christian Associations, and Tang Han, acting Cardinal of Hong Kong, had issued an urgent appeal for peace and the creation of an independent committee to find a way through the impasse. 

"The people of Hong Kong are extremely worried," they said.

"All parties must exercise restraint and avoid provocation. Regardless of your position, cherish life and never do harm to yourself or others.

"[We] call on the government to take the initiative to resolve the current difficulties with representatives of different sectors of society."

Lord Alton of Liverpool said at the US State Department's ministerial on religious freedom last week that it was "little wonder" that the people of Hong Kong were protesting, given China's track record on human rights.

"What a disgrace that we sell face reconstruction and other surveillance equipment to a regime that has incarcerated its own people," he said of the UK.

"Little wonder that millions of protesters in Hong Kong, fearful of losing their right to religious freedom and political freedoms have taken to the streets singing as their anthem, Hallelujah to the Lord.

"I salute the courage of the people of Hong Kong."

The Vine Church, based in the Wan Chai district of Hong Kong, said there was a "need for concerted prayer".

It has issued a special prayer for Hong Kong. 

Lord God,

We cry out to You for our city in its time of need. Please help those in authority to be humble and wise in their decision making. Help those who are demonstrating to be peaceful and considerate. Please restrain our anger and frustration from creating violence and harm. We need Your intervention to bring about a resolution to this present situation of unrest.

Bring comfort to those who are anxious, fearful, and confused by what they see happening around them. Lord, we ask that You listen to the cries of justice. Lord, without You this situation seems to be hopeless, so we ask for Your wisdom to prevail where human wisdom fails and political expediency takes precedence.

Show Your mighty arm of justice and righteousness in this place and bring about a peaceful outcome to rebuild this broken city.

In Jesus' name, Amen.