Public nudists have come under fire in Germany as Europe sizzles in temperatures of up to 45C in the heatwave dubbed the "Sahara bubble".

In Brandenburg, police posted two pictures of a man riding a moped naked and called for captions of the images.

"Because we're speechless," said police, adding the hashtags #heat, #safetyfirst and #livingontheedge.

As contributions and queries poured in over whether the man flouted any rules, police clarified that it was not illegal to go around nude in public, but only so long as no one files a complaint.

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In Germany's south, topless female sunbathers sparked a row after five fully clad security men walked over to tell them to put their bikini tops back on, Sueddeutsche daily reported.

Several other sunbathers nearby stood up for the women, and one told the newspaper: "We took off our bikinis out of solidarity."

As debate heated up, the Greens party brought the issue to Munich's city council.

"It's incomprehensible if men can lie in the sun topless but not women," said Dominik Krause, among the initiators of the council debate.

The CSU, conservative Bavarian allies of Chancellor Angela Merkel, took another view, and instead tabled an urgent motion requiring bathers to put on "swimwear that completely keeps their main sex organs covered" unless in an area specifically designated for nudists.