German weapons-maker Rheinmetall opened Europe's largest munitions plant on Wednesday, a move hailed as boosting Western defences by NATO chief Mark Rutte.

Taking up 30,000 square metres -- the size of five football pitches -- the factory in Unterluess in northern Germany will be able to produce 350,000 artillery shells a year by 2027.

"This is absolutely crucial for our own security and also to keep supporting Ukraine in its fight today and to deter any aggression in the future," Rutte said at an opening ceremony.

"We are being challenged" by China and Russia, he said, but added that Europe and the United States together are on course to "turn the tide on defence production".

Europe has moved to ramp up weapons production and military readiness following Russia's full-scale invasion o

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