Recent events in Berlin and Ankara are "unsettling", Prime Minister Bill English has said.

At least nine people have been killed and up to 50 injured when a truck ploughed into a crowded Christmas market in Berlin in what police suspect was an attack.

Earlier, a gunman wearing a suit and tie and shouting "Allahu Akbar" shot and killed Russia's ambassador to Turkey as he gave a speech at a photo exhibition.

Speaking to reporters after seeing his new ministers officially sworn in at Government House in Wellington, English said it was too early to "jump to conclusions".

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"But both of them are awful events that have occurred in public environments where people would otherwise feel safe.

"And particularly our sympathies are with the families, particularly with this significant number of deaths in Berlin. We will wait and see how the investigations unfold, but they are unsettling."

Asked if the murder of the Russian Ambassador could badly worsen relations between Turkey and Russia, English said it was too early to know.

"But you would hope that this kind of incident doesn't create anymore instability or friction in that relationship...it is always better without this kind of very tragic and unsettling event. Both in Turkey and in Germany.

"We have got to be careful not to overreact and second guess what the political consequences may be."