A sinkhole estimated to be around 10ft deep and several metres wide has appeared in the middle of a busy road in Bognor Regis.
Victoria Drive was cordoned off when the hazard appeared.
While the mouth of the hole has a circumference of a couple of feet, a Highways official said it was considerably bigger and deeper in size.
It was reportedly spotted by a cyclist on Monday. He alerted a neighbouring nursery school which helped to direct traffic away before police and Highways officials arrived to shut the road.
A woman who works at the Bognor Regis Nursery School and Children’s Centre, right next to where the sinkhole opened up, said: “Apparently the man who lives opposite it spotted something black and thought a bird had been run over.
“But it was a cyclist who happened to be going past who saw it, he grabbed our school sign and put it over the hole so no one would go over it.
“He came running into the school shouting ‘there’s a big hole in the road outside which is really dangerous, you’d better phone Highways’ which is what we did.
“It’s so lucky he saw it first, otherwise who knows what could have happened. It looks deep enough for a car to get stuck. How far down it goes I don’t know.
“Luckily it happened after most of the children had come in.”
Half of Victoria Drive remains closed from the roundabout joining Linden Road.
A West Sussex County Council spokesman said the sinkhole would now be opened up further to determine its size and what had caused it to happen.
He said: “It’s a couple of feet in diameter but that’s only the opening, underneath it’s considerably bigger. It looks to be about 10ft deep.
“We have made the scene safe, but obviously being in the middle of the road it’s not in an ideal position.
“It’s not an every day occurrence, but sometimes they do just open up, plus it’s a hot day so the heat on the tarmac could have caused it.
“We will now open it up further to investigate. It’s difficult to say how long that will take, but there was a sinkhole in Linden Road four years ago and the road was shut for a few weeks.”