"They don't want to leave the place; of course they don't want to. But they realise that realistically it can't remain."
The Assistant Anglican Bishop of Auckland, Jim White, said a decline in church attendance was common for most Christian groups in the Western world.
"The fact is that fewer people go to church. We all think about that and we all have our concerns about that. There are ... institutional concerns that you can't sustain the infrastructure, including buildings and even people's jobs, in a way that you once could.
"We've got our own responses to concerns about decline and sometimes we are aware we have to consider whether in fact keeping up a building and all that goes with it is the right thing."
However, Bishop White said his biggest concern was the decline in the number of people who engaged with religion.
Dr Geoff Troughton, a lecturer in religious studies at Victoria University in Wellington, said there was a lot of mobility between religions and churches had to compete to attract people.
"The more popular churches these days typically offer a wide range of services and activities and can be very busy centres," he said.
"Rather than seeking to maintain a presence in every suburb, the older denominations are often pooling resources in order to meet this demand.
"In some ways there is a lot of competition out there - but churches are also choosing not to compete everywhere."
Bayleys salesman Peter Christoffersen, who is marketing the Castor Bay property, said there had been interest from developers, daycare operators and other churches.
He said the block could be subdivided and standalone residential dwellings made of the church - which is thought to be more than 100 years old - and hall, which was built on the site in 1933.
Mr Christoffersen said a developer might want to remove both buildings to make way for a large modern home. Tenders close on October 25.
In the 2006 Census
* 1.29 million people had no religion - an increase from 29.6 to 34.7 per cent of the population
* 2 million people were affiliated with a Christian religion - a decrease from 60.6 to 55.6 per cent of the population
* 38,000 people were affiliated with Sikh, Hinduism or Islam - an increase of 53 per cent