The man who photographed a sign on a Dunedin beach claiming to prove the earth is flat is in shock after it made the headlines across the world.

Stephen Voss noticed the sign at St Kilda Beach while walking to Lawyers Head.

The sign questions why the horizon out to sea is "level" and points people towards a YouTube video claiming to prove the earth is flat. Voss, who works as a doctor in Invercargill but lives in Dunedin at weekends, posted a picture of the sign online, saying "it appears that the Flat Earth Society have infiltrated St Kilda".

Since then the story has been picked up by news outlets across the world, including The Sun, Daily Mail and IFLScience.

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He said yesterday he was shocked by how much media attention the post had gained.

"I wasn't expecting it would go anywhere beyond a few of my friends."

The media attention started when one of his Facebook friends, who is a reporter for the Daily Mail Australia, asked if they could use the post.

Most commenting on Voss' post ridiculed those who believed the earth was flat, but a few defended the theory, including one person who said "what you believe has only been pushed on the masses since Nasa was formed at the end of WW2".

Voss said there was not much point arguing with flat earth believers.

"It's pretty hard to follow their logic, really, and it seems that there is really no point in trying to negotiate with them because they are pretty fixed in their ideas."