TAP Air Portugal has apologised for leaving over 100 passengers stranded at Stuttgart Airport in southwestern Germany after cancelling a flight at the last minute because the co-pilot was intoxicated.

According to the New York Post, Flight TP523 was scheduled to depart from Stuttgart to Lisbon, Portugal, on the evening of March 23 when an airport worker noticed the co-pilot walking unsteadily and smelling of alcohol.

Airport authorities were alerted, and the decision was made to keep the plane grounded.

Aviation authorities determined that the 40-year-old was unfit to fly. He was detained and bail was set at 10,000 euro ($A15,600).

He was also asked to surrender his flying licence. Police declined to give any additional details.

All 106 passengers were given hotel rooms to stay overnight, German news agency DPA reported. There wasn’t a replacement crew available to fly passengers to Lisbon and the flight was rescheduled for March 26.

The pilot, who was determined to be in a “highly intoxicated condition” on Friday evening was found to be “reeking of alcohol and walking unsteadily,” according to an official statement released by German authorities.

German authorities did not name the airline but a flight of the Portuguese carrier TAP, due to leave Stuttgart for Lisbon on Friday night with 106 passengers, was cancelled.