"Demand has more than doubled," said a spokesperson for FlixBus, which operates intercity bus services across Europe.

The increase in bookings has been stronger than during previous strikes at state rail operator Deutsche Bahn, the spokesperson added.

Train drivers are set to strike from Wednesday morning until the following Monday evening, the GDL union's longest walkout yet in a months-long dispute over wages and working hours.

Deutsche Bahn has warned of massive disruptions to its network nationwide during the six-day strike.

Germany's flag carrier Lufthansa has seen "additional bookings for its domestic German flight connections and is deploying larger aircraft on various routes" to boost capacity, a spokesperson said.

Car rental companies Sixt and Europcar, which operate a network of 350 and 300 stations across Germany, respectively, also said bookings had increased for the coming days.

"We are currently observing a significant increase in demand throughout Germany this week," a Sixt spokesperson said.

(Reporting by Nette Nöstlinger and Rene Wagner, Editing by Rachel More)