A motorist has posted video of a campervan driver repeatedly crossing the centre line on a picturesque South Island road, apparently in an attempt to prevent following vehicles overtaking.

The three-minute long footage was loaded to YouTube by a user named stenly yesterday and been watched more than 500 times by this afternoon.

"Dangerous driving in South Island - Is this normal?", stenly asks.

We'd hope not.

The footage shows a large campervan being driven erratically on Braemar Rd, near Lake Tekapo, in the South Island's Mackenzie Country.

The vehicle crosses the centre line several times, prompting those travelling in the vehicle behind to speculate the driver was deliberately preventing them from passing.

The driver was travelling at speeds of between 40 and 45kmh, they said on the footage.

"We were heading from Lake Tekapo by Braemar Road towards campsites and this driver - not sure why - just does not allow us to over take him.

"Our way was crossed by his vehicle at the beginning of maneuver (sic). This almost caused an accident and us ending up in ditch!

"This is not normal when you drive on almost perfect conditions with no traffic at all in speed about 40km/h. Welcome in South Island, how is possible to have somebody like this driving such a big campervan?"