A father and son have been rushed to hospital after falling into a manure pit on a farm in Groningen, broadcaster NOS said on Saturday.

Both were unconscious when they were freed from the manure pit by firemen, apparently after being overcome by fumes. It is unclear how long they were trapped before the emergency services arrived.

NOS said the son, a teenager, may have fallen into the pit while working and his father fell in while trying to rescue him.

Accidents involving rotting farm manure, which contains hydrogen sulfide, methane, ammonia, and carbon dioxide, are not unknown in the Netherlands. In high concentrations, each of these gases may pose a health threat to both humans and livestock.

In 2013, three farm workers were killed after becoming trapped in a manure silo and in 2008 two men have been killed by fumes while working with manure on a farm in Friesland.