German Chancellor Angela Merkel has had another episode of uncontrolled trembling, a week after a similar incident that sparked questions about her health.

The latest episode came hours before she was due to board a plane for the G20 summit in Osaka, Japan.

The German leader began to tremble as she stood next to President Frank-Walter Steinmeier, who was giving a speech at a ceremony to formally appoint a new justice minister.

The shaking went on for two minutes, according to a DPA photographer who was present at the event.

Mrs Merkel folded her arms visibly in a bid to stop the trembling.

She brought it under control once she was able to take a few steps. She was offered a glass of water, but turned it down.

Her previous bout of shaking last Tuesday had been blamed on dehydration on a hot summer's day.

Despite the latest incident, a German government spokesman said Mrs Merkel would not be cancelling any appointments today and Friday.

"The chancellor is well," he said, adding that she will be flying as planned to Osaka for the G20 summit.

Mrs Merkel turns 65 next month and has said she will leave politics at the end of her term in 2021.

There were brief concerns about her health in 2014 when she was taken ill during a television interview.

The broadcast was briefly interrupted when she experienced a drop in blood pressure.

Her spokesman Steffen Seibert explained at the time the leader did not feel well for a moment, then ate and drank something and continued the interview.