A 100 metre deep sinkhole full of water has opened up in a Brisbane backyard.

Rescuers reach the injured caver who fell at the 176 metre deep sinkhole this afternoon.

Though covered with reeds and sedge, the small field turned out to be a deep sinkhole of waterlogged clay and silt.

The 35-metre deep sinkhole was discovered in July after an unexplained eruption that flung soil and rock 120 metres from the site.

Through these deep sinkholes, the deceased were thought to pass into the dark and treacherous underworld of Xibalba, where humans and deities were reborn.