Robert Enke died close to his home in Neustadt-Eilvese, Hannover, near a railway level crossing. "First indications point to suicide," a media officer for the Niedersachsen police said.
"At 1825 (1725GMT) he was run over by a regional express train running between Hamburg and Bremen," said police spokesman Stefan Wittke. "The train was travelling at the speed of 160-kph."
Robert Enke's friend and consultant Joerg Neblung told reporters: "I can confirm this is a case of suicide. He took his own life just before six (pm). There will be a press conference tomorrow with more details".
Robert Enke won eight international caps and was in the running to play at the World Cup in South Africa next year. However, he missed Germany's last three qualifiers with a stomach virus and having just returned to action after almost two months out was omitted from the latest squad.
His national team colleagues learned of the tragic news of his death after training in Bonn on Tuesday and Germany's general manager Oliver Bierhoff said: "We are all shocked. We are lost for words."
The president of the German Football Association (DFB) Dr Theo Zwanziger added that he and the rest of the football community in Germany "are deeply distressed and in mourning".
"All our sympathy goes to the wife of Robert Enke and his family," he added.
It is not yet clear whether Germany's friendly against Chile on Saturday will still go ahead. Die Mannschaft are due face the Ivory Coast the following Wednesday.
Hanover president Martin Kind said: "This is a tragedy."
Enke, born in Jena in the former East Germany, also played club football for Borussia Moenchengladbach and Benfica and had a brief spell at Barcelona before stints with Fenerbahce and Tenerife.
Enke's daughter Lara died in 2006 of a rare heart condition when she was just two. He leaves behind his wife, Teresa, and an eight-month-old daughter the coupled had adopted.