Protesters from a far-right group have interrupted a church service dressed in mock Islamic dress to grandstand about the so-called “Muslim invasion” of Australia.

The Party for Freedom targeted Gosford Anglican church on Sunday to claim its leadership was assisting the “invasion” because of its support for social justice causes, including its progressive stances on multiculturalism and refugees.

The group posted videos and photos on their Facebook page which show them being questioned by police and then celebrating in a nearby pub.

Father Rod Bower has blasted the group for frightening children and the “sacrilege” of violating the religious space.

As part of the demonstration, the group, which supports Pauline Hanson’s One Nation, criticised the Labor and Liberal parties for allowing immigration from Muslim nations.

Hanson has labelled the demonstration “counter-productive” and warned media not to blame her for it.

A photo posted to Party for Freedom’s Facebook page shows police questioning members of the group on Sunday after they interrupted a service at Gosford Anglican church

The group posted a video showing about 10 people clothed in ankle-length tunics including thawbs and niqabs walk into the church past its message board, which read: “Good luck to Aussie & refugee Olympic teams.”

Once inside, one man said they were sharing the “rich tapestry of Islam” with Bower and his congregation because of their support of the “social justice agenda”.

The group set up prayer mats and played audio of the Qur’an being sung. “This is the future brothers,” he said as the congregation looked on in confusion.

“You asked for it, you voted for it, you supported it … a Christian congregation support[s] the Islamic invasion.”

Bower also recorded video of the event, and took to Twitter to accuse the group of “impersonating Muslims, interrupt[ing] service … [and] frighten[ing] children”.

Churchgoers turned their backs on the group while they spouted anti-Islamic messages accusing adherents of Islam of slaughtering Christians.

“Just in case you’re wondering – these people actually aren’t Muslim … This is what I talk about as being radicalised Christianity, so we’ll deal with it,” one church leader said.

After a few minutes, the group left, warning the congregation not to “promote Islam”.

Party for Freedom members pictured in the pub after their stunt at the Gosford church. Photograph: Party for Freedom Facebook page

Bower told ABC News24 the intrusion was “a gross violation of our sacred space and quite traumatic for many of the people in the congregation”.

“It was a gross violation of when Christians meet together on a Sunday morning, it’s an act of love, it’s a very intimate thing we do, we break bread together, and to have that action of hate to come into that space, it’s sacrilege, really.”

He said he surmised the group had targeted his church because of its work for refugees and social equality.

“We do a lot of work to build bridges rather than walls and I’m afraid these rightwing extremists really want a dysfunctional society.”

In another video depicting the group praying outside, a man says: “This is the future … keep voting Labor and Liberal and this will be the future.”

“You are being replaced, with mass third world immigration and Islam coming into Australia to take over,” he said.

Hanson told Guardian Australia: “There are concerns by a cross-section of Australians with Islam, border protection, terrorism and the government’s immigration policy.

“However the interruption of religious services, as demonstrated online, [is] counterproductive in the serious argument One Nation [is] calling for in our parliament.”

She warned it was “uncalled for” to blame One Nation for the demonstration.

“Let’s have a proper debate as a community and leave the satire out of it.”

The stunt came after a new push by crossbench senators to overhaul the Racial Discrimination Act by removing a restriction that prohibits insulting or offending people based on their race, section 18C.

Bower said the display highlighted the need for the section. “If you lose 18C then this kind of vilification and abusive behaviour will go even more unchecked,” he said.

Senator David Leyonhjelm was asked about the demonstration on ABC News24 in the context of his push to repeal section 18C. He replied: “Well, there’s an awful lot of issues there outside of free speech.”

“Apart from trespass, of course. Interruption of a church service would raise other issues.”

Guardian Australia is seeking comment from the Party for Freedom.