The emergency services were called out after the vehicles – a white Fiat 500, silver Renault, red Mercedes C-Class and Green Honda – collided close to the junction with Rue du Galet shortly after midday.
There were unconfirmed reports that the accident may have occurred after one of the drivers suffered a seizure at the wheel.
The accident left several cars severely damaged – and the white Fiat 500 came to a rest facing the wrong way on the westbound carriageway.
Witnesses reported seeing a man being treated on the ground as both lanes of the westbound carriageway were closed.
The accident caused severe disruption, with traffic backed up to the Underpass. The road reopened about an hour after the accident.