Lufthansa stocks fell sharply after reports emerged that a plane operated by Germanwings, the group's budget airline, had crashed in a remote part of southern France.
Initial reports said there were 144 passengers and six crew members on board the Airbus 320, which was travelling from Barcelona to Dusseldorf.
French President Francois Hollande said he believed everyone on board had been killed in the crash. "There are not thought to be any survivors," he told reporters.
Shares in the German airliner fell from $14.06 to $13.32 at 12.10pm in London. Meanwhile, shares in Airbus, the plane manufacturer, fell $60.70 to $58.79 at 12.20pm GMT.
Lufthansa chief executive Carsten Spohr said it was a "dark day" for the company and offered his "deepest sympathy" to the families and friends of the passengers and crew.
The Airbus A320 is one of the most popular models of passenger plane in the world for short and medium-haul flights. The single-aisle aircraft has a capacity of up to 180 people.
The last A320 crash was the AirAsia flight QZ8501, which crashed in December 2014 en route from Surabaya to Singapore, killing all 162 people on board.