Germany's famed speed-limit-free motorways zoomed to the top of the political agenda Wednesday when an opposition leader called for restrictions to help cut accidents.

Sigmar Gabriel, head of the centre-left Social Democrats who are battling to unseat Chancellor Angela Merkel in a September 22 vote, demanded a 120-kilometre (75-mile) limit.

He told the daily Rheinische Post the move was "sensible" because figures showed it reduced serious accidents and deaths, adding: "The rest of the world has long been doing it this way."

Transport Minister Peter Ramsauer however rejected setting 120 kilometres as a limit on motorways and said the worst accidents happened on regional highways anyway.

"With me, there will not be a general speed limit on Germany's motorways," he told the online edition of news weekly Der Spiegel.

"Our motorways are among the safest roads," he added.

Around 60 percent of traffic deaths occur on regional highways, he said, citing current traffic statistics.

He also said that almost 40 percent of Germany's 12,800 kilometres of motorway have permanent or temporary speed limits anyway. These apply to dangerous stretches or where construction is underway.

But from within Gabriel's own party, its candidate for chancellor Peer Steinbrueck appeared sceptical about the introduction of a speed limit, telling public broadcaster WDR he had no intention of re-igniting the debate.

Germans are fond of their high-speed cars and limitless autobahns and the subject of imposing restrictions regularly stirs debate, with the ecologist Green party backing the move as a way to cut emissions.