One of Melbourne's oldest churches will have to close if urgent repairs aren't made, says a conservation architect.

A campaign is being launched to raise $4.6 million to save St Kilda's Christ Church, which is riddled with crumbling stone, with leaking roofs and gutters.

Nestled amid houses and flats in a quiet part of Acland Street, the much loved landmark, opened in 1857, is believed to be one of the few surviving buildings made from sandstone quarried at Sorrento's Point King. 

The Victorian Heritage Register says the building "demonstrates outstanding craftsmanship" for its triangular rose window, its lofty chancel with gold leaf wall stencilling; timber trussed ceiling; and "fine and varied collection of stained glass".

Specialist heritage architect Arthur Andronas​, who has conducted two audits of the Anglican church in the past 15 years, said it was time to act to save the church from ruin.

"If nothing is done in five years, the church will most likely need to be shut down because of the public risk, from collapsing stone in particular, and slate slipping off the roof." 

Already plaster is crashing through the inner vestry's ceiling, and one porch door is permanently closed because its stone frame is falling off.

The church's inside walls cannot be painted, because of rain leaking in. The damp is also weakening the walls and rotting timber roof beams.

Former Port Phillip deputy mayor Serge Thomann, who lives near the church, said it was one of the oldest public buildings south of the Yarra, "and we need to save it for generations to come". 

"If nothing gets done, if it continues to get put on the backburner, then eventually the place will fall into disrepair and have to close."

Valerie Lion, 76, a parishioner since 1969, said she would be "distraught" at the closure of the church where she volunteers and where her son was christened in 1975. "It's part of me," she said. 

She says the church "will start to fall down" soon and was in a "parlous" state. She said developers would love the land for apartments, but a vital community hub would be lost.

The church's 160th celebrations will double as an awareness-raising for the Restoration Appeal.

Next Friday, Saturday and Sunday from 5.30pm to 11pm there will be a light show projected on the church, plus a historical display and musical performances inside.

On July 29 and 30 the church will be open from 1pm to 4pm for Open House Melbourne.

On July 30, Melbourne Archbishop Philip Freier​ will take a communion service.

There will be a further concert and historical display on August 4. Donations are tax deductible through the National Trust.