Aitutaki
© NASA / Wikimedia CommonsSatellite image of Aitutaki.

A tiny Pacific island famed for having the most churches per capita in the world is reeling after its first-ever bank robbery.

The residents of Aitutaki, a peaceful tourist escape in the Cook Islands, have been shocked by a brazen theft from its tiny bank, which has left them up to $US164,000 ($157,000) poorer.

The island's mayor John Baxter told Radio New Zealand International he believes the heist was not carried off by one of the 1800 locals, most of whom kept their savings at the branch.

"It's a very sad occasion or event that has happened," Mr Baxter said.

"I think it is the first time that any of the banks have actually ever been robbed on this small island of Aitutaki and, as I said earlier on, everybody knows everybody and I suspect whoever has done this does not live on the island."

Few details have been disclosed about the Bank of the Cook Islands robbery, which was believed to have been carried out one night last week.

Police Commissioner Maara Tetava said a large amount of money was stolen but would not confirm the bank was only secured by a single padlock.

The branch and two other banks have stepped up security since, he said.

As one of the first places in the South Pacific to accept Christianity, Aitutaki has always been celebrated for its piousness.

The island, just 18sq km, has more than 20 churches from more than a dozen faiths, including Protestant, Mormon, Roman Catholic, Seventh Day Adventist, Baha'i, Apostolic, Assembly of God and Jehovah's Witness.

Islanders are so devout that tourists cannot arrive or leave the island on a Sunday and no tourism activities operate for the day.