A giant crater appeared overnight just metres from a busy road and locals feared a meteorite had crashed into Earth.
The huge 9-metre-wide hole was spotted by walkers just over a hedge from the busy road leading to a housing estate.
It was at least 2.7 metres deep and council officials were called in to look into it.
Now officials in Caerphilly, South Wales, believe the sinkhole was caused by old mine – and not an alien invader from outer space.
Walker Penfold Brindle was amazed at the crater-like hole on common land near Graig-y-Rhacca housing estate in Caerphilly.
"It was absolutely huge – it is a good job it wasn't a few yards away under the road. It would have swallowed any car which went into it," he said.
"Something needs to be done to fix hit. They have put a fence around it and a few cones."
Local social media groups were stunned at the size of the hole. One said: "Have we had an alien invasion? Dr Who were filming nearby and I think a Cybermen attack is on the way."
Another said: "Watch out for little green men – and I don't mean the council rubbish collectors."
"The village used to be a coal mining village. It's all just a matter of time," a local added.
A spokesperson for Caerphilly Council said: "Our officers have been liaising with the Coal Authority as it falls under their responsibility. We understand that they have fenced off the area and taken action to reduce surface water in order to make it safe, whilst formulating plans for a permanent solution."
Zoe Rose-Higgins, head of public safety and subsidence at the Coal Authority, said the Coal Authority was made aware of a ground collapse at land just off Addison Way Road, Graig-Y-Rhacca, Caerphilly.
"We are working closely with Caerphilly County Borough Council to make the site safe and carry out thorough investigations to determine the cause," she said.
"If this incident was caused due to historical coal mine workings, we will design a permanent solution and carry out repair works as soon as we can."
Do you have a story tip? Email: email@example.com.