The sinkhole, or tomo, was about 200 metres long, 30m wide and 20m deep, farm manager Colin Tremain said.
It runs along a fault-line at the Tumunui farm and was discovered by one of the farm’s staff, who went out to get the cows first thing on Monday morning.
Tremain said he would put a fence around it because it was a waste of time trying to fill it in.
“There was one around the other side, I was watching it in the rain, huge amounts of water going in, it wasn’t even filling up with water, it’s just going straight out the bottom.”
The tomo would get even bigger because there was already a crack which extended 400 to 500 metres through the property, Tremain said.
The farm had 146 millimetres of rain over a 24 hour period on Sunday.