Spanish police are investigating a mystery tunnel found running under a city.

The Guardia Civil entered the newly uncovered underground structure for an inspection in Ceuta on Wednesday, February 19.

The passage was found during an operation targeting hashish trafficking. It was located during a search of a warehouse in an industrial area.

Authorities said the tunnel stretched at least 50 metres (164ft) with multiple galleries beneath Spanish territory and plunged to a depth of 12 metres (39ft).

Its cramped dimensions, measuring just 40 centimetres wide and 60 centimetres high, vary slightly depending on the section, hinting at a complex design.

Footage shows officers crawling through the narrow path, carefully inspecting the tunnel to gather evidence and unravel its intended use.

The Guardia Civil said the narrow passage could have been used to transport drugs across the border between Morocco and Spain.

No drugs were found at the site, and no arrests were made during the discovery.