Cladding on the ceiling of the Regional Road tunnel fell off last night, fortunately missing cars driving through.
No one was injured but motorists reported seeing stones and concrete on the road before the tunnel was temporarily closed for inspection by a government architect.
The incident happened at about 2am.
Traffic was briefly diverted but the tunnel has now reopened. The damage did not appear to be serious.
The tunnels were inaugurated on September 18, 1971 by Works Minister Lorry Sant after having been built as part of the Regional Road project by the Borg Olivier government.