A sign planted at a Dunedin beach claiming to prove the earth is flat has been covered by news outlets across the world.

Dunedin man Stephen Voss spotted the sign, which questions why the horizon out to sea is "level" and points people towards a YouTube video claiming to prove the earth is flat, while walking to Lawyers Head.

He posted a picture of the sign on Facebook and saying "it appears that the flat earth society have infiltrated St Kilda".

"Funny how they equate doing research with watching YouTube videos!"

Since he put the post up last week it has been picked up by news outlets across the world, including The Sun, The Daily Mail, LADBible and IFLScience.

Most commenting on the post by Mr Voss riduculed those who believed the earth is 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".

The video the sign's author suggests people view is titled "200 Flat Earth Proofs", runs for two hours, and claims to debunk the "mother of all conspiracies" and prove the earth is flat.