It is believed the bus smashed into a row of several trees, which ripped apart the front of the bus.
Shocking images from the scene in Eskisehir show the vehicle has crumpled to one side as it leans into the row of trees.
Glass from the front window lies shattered on the floor, with the metal roof in tatters having collapsed into the vehicles.
Fire crews raced to the crash, working frantically to remove those who survived the horror smash.
The bus was travelling overnight from the capital, Ankara, to the Uludag resort near the city of Bursa when it crashed on what were said to be good road conditions, reports say.
Eskisehir governor Ozdemir Cakacak said it was not clear what caused the accident as the road was not wet or frozen.
Earlier reports suggested the death toll in the incident was as high as 13 but Cakacak maintained the death toll as 11.
He added: “I wish Allah’s mercy on our citizens who have lost their lives and a speedy recovery to the injured,” he said.
“The accident is currently under investigation.”
Those injured were currently being treated at three different hospitals, he added, but it is not known if there are any children among the victims.
The two drivers have been arrested, and an investigation has been launched.
Turkey has a poor track record in road safety, with more than a million accidents in 2016 and 7,300 deaths.