WINNENDEN, Germany (Reuters) - A 17-year old gunman went on a shooting spree at his former school in southwest Germany on Wednesday, killing up to 15 people before dying himself in a shootout with police, authorities said.

The former student, dressed in black combat gear, entered the school in Winnenden, a town of 27,000 near Stuttgart, at around 9.30 a.m. (3:30 a.m. EDT) and began firing.

He killed nine students and three teachers at the school, as well as one person at a nearby clinic, before fleeing with a hostage in a car. He was killed in a shootout with police.

Two additional passers-by were killed and two policemen seriously injured in the shootout, bringing the total death toll to 16 including the gunman.

It was not clear whether the gunman had been shot by police or taken his own life, Rainer Koeller, a police spokesman in nearby Waiblingen said.

I've been president of police in Baden-Wuerttemberg for 19 years now, and I can't remember a deed as terrible as this, said Erwin Hetger, police chief in the southwestern state.

A German government spokesman in Berlin said he was deeply shocked by the incident. Chancellor Angela Merkel would make a statement at 4 p.m. (10:00 a.m. EDT).

The shooting is the latest to shock Germany in recent years. In 2006, a masked man armed with rifles and explosives attacked a school in the western town of Emsdetten, wounding at least 11 people before committing suicide.

In April 2002, Germany suffered its worst school shooting when a gunman killed 17 people, including himself, at a high school in the eastern city of Erfurt.

Police said the gunman had entered two classrooms at the Albertville-Realschule in Winnenden and probably opened fired at pupils indiscrminately.

The secondary school is for students aged around 10 to 16. It was evacuated and rescue workers and fire fighters were at the scene. Helicopters circled above the historic market town, which had been largely sealed off.

Television pictures showed dozens of heavily-armed black-clad SWAT teams entering the two-storey white school building.

Police are coming through the whole time. They're obviously looking all over town for him, said Roberto Seifert, who works at a company neighboring the school. We've never had anything like this, he told Reuters.

German media reports said the suspect had used weapons his parents legally held at home, although police could not confirm this.

Germany has strict weapons laws, with gunholders having to fulfill certain criteria on age and weapons expertise to obtain a license for firearms.

A market town whose origins stretch back to the 12th century, Winnenden is the hometown of German firm Kaercher, a maker of high pressure cleaners.

(Reporting by Holger Hansen, Dave Graham, Noah Barkin; Editing by Richard Balmforth)

(Writing by Kerstin Gehmlich; Editing by Angus MacSwan)