Merkel was at the headquarters of the country's presidency attending an official handover ceremony between Justice Ministers along with Germany's head of state, Frank-Walter Steinmeier.
Media footage shows the Chancellor, who turns 65 in July, holding onto her arms in an apparent bid to quell the shaking and turning down a glass of water offered to her by an assistant, Efe news reported.
Last week, Merkel played down speculation over the state of her health after she suffered a similar episode while receiving Ukrainian President Volodymyr Zelensky during an official welcome ceremony in the German capital on June 18.
It had been a hot day in Berlin and the Chancellor was seen trembling for about half a minute as she stood next to Zelensky as the German national anthem rang out. That incident garnered much attention from local news media and beyond.
"I'm fine, I drank at least three glasses of water," Merkel said of the incident. "Now I feel good again."
Merkel attributed the shaking to being dehydrated when asked about it during a joint press conference with the Ukrainian head of state.
Unlike the ceremony with the Ukrainian President, which took place outdoors in the courtyard of the Federal Chancellery, Thursday's ceremony was held inside the Bellevue Palace.
Christine Lambrecht replaced Katarina Barley as Justice Minister during the event.
Germany, like much of Europe, has been gripped by a heat wave with temperatures of almost 39 degrees Celcius recorded on Wednesday. The heat was expected to wane in next two days, before picking up again at the weekend.
Merkel is expected to travel to the Japanese city of Osaka later in the day to participate in a G20 meeting with other world leaders.
She has been the Chancellor of Germany since 2005.
( With inputs from IANS )