Angela Merkel and Antti Rinne walk after listening to the national anthems at the Chancellery in Berlin on Wednesday. Tobias Schwarz / AFP

German Chancellor Angela Merkel suffered her third trembling spell in less than a month on Wednesday that revived questions about her health.

However, after the incident she insisted she was "very well."

Merkel began shaking involuntarily as national anthems were being played at the reception of Finnish Prime Minister Antti Rinne.

But she attended a press conference as planned just around an hour later, telling journalists that her health was no cause for concern.

"I feel very well, there is no need to worry," she said, adding that she was simply still in a phase of "processing" a previous shaking spell, but that "there has been progress".

"I must now keep going with that," added Merkel, who turns 65 next week.

A source close to the government had said the cause of the repeat shaking was now psychological, with memories of the first incident provoking renewed trembling at events with similar settings.

The shaking on Wednesday was visible although less severe than during the first episode in June.

On that occasion she appeared unsteady and shook as she stood in the midday sun next to Ukrainian President Volodymyr Zelensky, whom she was welcoming with military honours.

That first bout of shaking was blamed on dehydration, but a second episode struck a week later at the end of June, just hours before she was due to board a plane for a G20 summit in Japan.

Officials had sought to play down fears over her health then, saying that she was fine and that she would not be cancelling any planned engagements.

Merkel, who has been leader of Europe's biggest economy for almost 14 years, has always enjoyed relatively robust health.

Frequently called the European Union's most influential leader and the most powerful woman in the world, Merkel has said she will leave politics at the end of her term, in 2021.

But she has struggled to stamp out repeated speculation that she may leave the political stage earlier than planned.

Agence France-Presse