At least five people were killed and more than 20 others were injured in a collision on a highway near the eastern German city of Leipzig.
The FlixBus bus veered to the right on the busy A9 motorway before falling onto its side.
The company confirmed that the bus left Berlin with two drivers and 53 passengers on board and was on its way to Nuremberg on its way to Zurich.
Saxony officials said their hearts were with the victims.
FlixBus, founded in Munich in 2011, operates a network of long-distance bus services in Europe, America and Asia.
The company said the accident occurred around 10:00 (09:00 GMT) on the A9, the north-south highway from Berlin to Munich. Service bus No. 107 was two hours into its southbound journey at the time of the accident at an intersection near Leipzig/Halle Airport, to the northwest of the city.
Police told German media that no other vehicle was involved in the accident.
“The exact circumstances of the incident are not yet known,” the company said in a statement, adding that the long-distance service was operated on behalf of FlixBus. “Our thoughts are with everyone affected by this incident and their families.”
Police said that rescue helicopters and a large number of ambulances were called to the scene immediately.
Local hospitals were told to prepare for a major emergency. Both lanes of the highway were closed near the Schweitzer Cruise Interchange. The rescue operation is expected to continue until the evening, police said.
Buses have been involved in accidents in the past on the A9 motorway near Leipzig, most recently in December. A woman was killed in a bus accident on the A9 motorway in 2019, about 20 kilometers (12 miles) south of the scene of Wednesday's accident in the state of Saxony-Anhalt.
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