At least 10 school children and a few other bystanders were killed when the black-clad man – said to be a 17-year-old former pupil – entered the Albertville vocational school in Winnenden at around 9:30am on Wednesday.
He reportedly said nothing before starting to shoot wildly and randomly around himself before heading into the town, which is located some 20 kilometres northeast of Stuttgart.
Reports of the man's age are contradictory, but a police spokesman has told reporters that they know who he is and the fact that his parents legally own 18 firearms.
“We still have to establish the facts,” a police spokesman said.
The around 1,000 pupils at the school were evacuated as rescue services flooded into the town of 27,000, as attention turned to the whereabouts of the shooter.
The authorities have now closed down parts of Winnenden's centre and warned drivers in the area not to pick up anyone as the man is considered armed and extremely dangerous.
“The town is practically sealed off,” the spokesman said.
Germany has been shocked by a number of fatal school shootings in recent years.
In February 2002, a 22-year-old gunman killed the headmaster and seriously injured another person in a vocational training centre he attended at Freising, near Munich.
Two months later, 16 people were killed at a high-school in Erfurt in eastern Germany, by a 19-year-old former student, who then killed himself.
In November 2006, a former student at a vocational school in Lower Saxony in northwestern Germany went a shooting spree in the establishment, injuring 37 people before turning his gun on himself.
The authories have set up a hotline for family members seeking information: 0711 904 40949