The incident occurred early on Sunday in the village of Valle Aurina, north-east of Bolzano in the region of Alto Adige, as the Germans gathered near a shuttle bus they’d been travelling on.
Witnesses said the car was going so fast that the force of the impact threw some of the tourists several yards into the air.
The victims were aged between 20 and 25.
Among those killed was a 23-year-old medical student based in the northern German city of Hamburg; a 22-year-old who played football for the German club of Siegen; and a 22-year-old architecture student from Cologne.
The 21-year-old woman was reportedly one of two who had been airlifted to a hospital in nearby Austria in a critical condition, Bolzano police said.
Police on Sunday said six people died at the scene and 11 were injured.
There were no immediate details on Monday on the conditions of the others.
The 27-year-old local man who was driving the car was taken to an Italian hospital after the accident but was soon released and taken to prison.
Italian media reported on Monday that the man had since been admitted for psychiatric care.
Prosecutors said the driver was suicidal after realising what he had done following the crash, Italian daily Corriere della Sera reported.
Police said he was charged with manslaughter and faces a possible 18-year sentence if convicted.
Italian news reports said the driver’s blood alcohol level was allegedly nearly four times the legal limit.
Several relatives of the victims visited the site of the accident on Monday, while well-wishers have left candles, flowers and messages at the scene.
Both German Chancellor Angela Merkel and Italian Prime Minister Giuseppe Conte have expressed their sympathy for the families of the Germans caught up in the accident.
Early on Monday, two women aged 34 and 40 were killed in another road accident, this time in the western Italian port town of Senigallia, on the Adriatic coast.
The two women had just left a disco and were walking on the side of the road when they were hit by a driver who tested over the limit for alcohol.