Several people have been injured by a suspected tear gas attack at Frankfurt Airport in Germany.

Witnesses said the check-in area at Terminal 1 was affected on Monday morning.

Police said six people were being treated for breathing problems after the incident at the country's busiest airport.

"The cause is unclear, investigations continue," a spokesperson added.

Frankfurt Airport operators said the fire brigade's operations had ended and found no "harmful substance" in the departures hall.

Check-in has reopened and flights are operating as normal.

The incident came less than 48 hours after a bomb scare caused a partial evacuation at Frankfurt Airport.

A man who was believed to be suffering from mental illness told police he was carrying explosives in his luggage but none were found.

A taxi driver had alerted officers about the 37-year-old's strange behaviour and they met him as he arrived at Terminal 1 on Saturday evening.

Local reports said the man was already known to police and has been taken to a psychological ward.

A previous alert was sparked on 31 August after a passenger entered a secure area before completing security checks.

Germany remains on high alert following an Isis-linked terror attack that killed 12 people in December and atrocities across Europe.