The German potash mine operated by K+S where three workers died from carbon dioxide poisoning may have to close for weeks, the fertiliser company's chief executive said.

The deadly blast happened on Tuesday Oct. 1 after a controlled explosion at the mine in the German state of Thueringia caused a blowout of CO2, which occurs naturally in the salt rock.

It may take "from days to a few weeks" to fan the gas out of the mine and for mining authorities and public prosecutors to complete their investigations, Chief Executive Norbert Steiner told Reuters.

The mine accounts for almost 1 million tonnes of the group's annual output in potash products of 7 million, according to the company. The accident occurred in a 700-metre-deep shaft near the town of Unterbreizbach. Four other miners were rescued.

Carbon dioxide occurs in pressurised liquid form in potash deposits that are mined using controlled explosions and when it vaporises, it expands 100 times in volume. The gas flooded the entire mine within seconds of the blast, causing a plume of salty dust to shoot up the mineshaft about 11 km (7 miles) from the site of the blowout.