A visitor has plunged into a deep hole made to look like a cartoon painting, currently on exhibit at a museum in Portugal.

The art installation, Descent Into Limbo by Anish Kapoor, was designed to look like an inky void and is an optical illusion.

Visitors to the exhibit at Serralves Museum in Porto, often questioned whether there was a hole in the floor or whether it was simply a painted circle.

The installation does include a hole, which is 2.5m deep as one unlucky visitor discovered.

The installation was surrounded by warning signs at the time but there was no physical barrier around the hole.

A man is his 60s was briefly hospitalised after he fell in according to Publico, and the museum has closed the exhibit while it investigates what happened.

It's unclear at this stage how he came to step into the hole.

Mr Kappor is known for his physics-defying works.

Newshub.