It swept past its $10,000 fundraising target and now an atheist campaign plans to double its contentious advertisements on buses.

New Zealand Atheist Bus Campaign spokesman Simon Fisher said the response to the campaign had been overwhelming and mostly positive.

The advertisements with the controversial slogan: "There's probably no God. Now stop worrying and enjoy your life", had rallied non-believers. By 3pm yesterday a $10,000 target had been reached – about 30 hours after the campaign had been launched.

The donations had been "rolling in fast" and the group had now doubled and capped the target to $20,000, he said. It would pay for advertisements on 12 buses in Auckland, eight in Wellington and four in Christchurch, each staying on the buses for four weeks.

Mr Fisher said the reaction had been far beyond his expectations and the new adverts could be on buses as early as January.

"Lots of people are asking `how can we help' and saying `finally we have something like this in New Zealand'."

Archbishop John Dew, president of the New Zealand Catholic Bishops Conference, said those behind the atheist bus campaign had the right to express their views.

"Freedom of speech is a right we all have. I find it interesting that a group of people who claim not to believe in the existence of God have chosen to make God the focus of their bus campaign."

The use of the word `probably' suggested a degree of uncertainty on the part of organisers. And as for enjoying life, the Gospel was about spreading good news, he said.

The campaign website states the word `probably' supported the view that "although there was no scientific evidence for God's existence, it's also impossible to prove that God doesn't exist".

Yesterday, the campaign sparked debate and divisions – even between Christians – on the Stuff website, with more than 300 comments. Evan wrote: "love it! where can we fund more messages!"

But Srassy said: "I'm a Christian and I'm all for the billboard as it encourages proper discussion."

Another wrote: "This is brilliant and the good news is; the campaign will find more people seeking God ... Thanks atheists. God knows you've tried."