At least four tourists have been injured, one seriously, after an open-top bus hit a low bridge in Paris. Emergency services have closed part of the road under the Pont Alexandre III.

The double-decker tourist bus hit the top of the tunnel under the bridge Alexandre III in the heart of Paris around 12.30pm local time.

According to the fire authorities one person is in a critical condition.

A police source said at least 18 people were "caught up" in the accident, BFM TV reports. All passengers have now been rescued from the bus.

According to French newspaper Le Parisien the bus driver tried to enter the tunnel under the bridge, which is forbidden to vehicles higher than 2.70 metres.

The bus company Big Bus Tours said the bus had taken the tunnel because other routes were closed as Paris shows off its sporting ways as part of its candidacy for the 2024 Olympic Games.