Authorities are investigating the origin of a foul smell that caused passengers on a Germanwings flight to feel sick shortly after the plane's departure.

The Airbus 319 was carrying 142 passengers and five crew members from Hamburg to Stockholm on Sunday (29 January) evening. After the smell was detected and passengers started feeling unwell, the pilot cancelled the flight and landed back to Hamburg.

According to the Hamburg Fire Brigade, six people reported having trouble breathing and experiencing nausea.

Three crew members were taken to a hospital with respiratory irritation. The three other passengers received medical assistance at the airport.

The cause of the smell remains unclear. "The investigations are still ongoing," said a Germanwings spokesman, as quoted in the local media.

The Cologne-based Germanwings airline is owned by German aviation giant Lufthansa. In 2015, Germanwings flight 4U9525 crashed into the French Alps after the co-pilot brought down the plane in an apparent murder-suicide. There were no survivors.