Nigeria’s environment agency has launched an urgent investigation after a strange white foamy substance appeared on a major highway, causing a public spectacle and raising safety concerns.

The National Environmental Regulations and Standards Enforcement Agency (Nesrea) has warned people to stay away from the unidentified substance along the busy Kaduna-Abuja highway, which links the main northern city to the federal capital.

Hundreds of motorists have stopped to photograph it since it appeared a few days ago, and many of them have shared images on social media.

Some speculated that it could be a chemical spill, while others seemed to revel in the novelty of the scene.

A regular driver on the route, Isah Aminu, told the BBC that he had initially been told by another driver that “clouds had fallen from the sky”.

“That was the first information many of us received: that these are clouds from the sky,” he said. “But like many, I also stopped to see it and it looked like snow,” he said.

Aminu said she was afraid to touch the foam, but noticed many others approaching her.

“I think the authorities should come out and explain what it is so that the confusion among people disappears,” he added.