Merkel, 64, was attending a ceremony to decommission Justice Minister Katarina Barley, who is leaving to become a lawmaker in the European Parliament.
She was offered a glass of water, but did not drink it.
A spokesman for the German leader dismissed any concerns over her health. "The chancellor is doing fine".
Yet her office has sought to calm nerves over Merkel's second bout of trembling in as many weeks, saying the veteran leader was en route to Osaka as planned for the G20 summit.More news: Royal split: Prince William, Harry drift further apart in charity move
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Merkel was due to set off for Japan later Thursday for the annual summit of the Group of 20 global powers.
Asked about Merkel's latest shaking episode, Interior Minister Horst Seehofer told reporters: "I won't comment on this".
Hot weather in Germany has continued this week, though outdoor temperatures in Berlin dropped significantly overnight after peaking at around 37 degrees Celsius (99 Fahrenheit) on Wednesday.
This was not the first time Merkel has been seen shaking under similar circumstances in the hot sun, according to the dpa news agency.
Mrs Merkel was previously filmed trembling while standing next to Ukraine's President Volodymyr Zelensky eight days ago.
Earlier that same year, she had fractured her pelvis while cross-country skiing in Switzerland and was ordered to cut back her schedule dramatically and stay in bed as much as possible for three weeks.
She has been chancellor since 2005, and presided over Germany's powerhouse economy that has propped up the eurozone through a series of crises.