Mahuta is currently in Europe, and was in Paris overnight attending a forum on the Indo-Pacific.
Prime Minister Jacinda Ardern said New Zealand had "called in the Russian ambassador to send a very clear message around New Zealand's position on what is happening in the region".
"Ukraine's sovereignty and territorial integrity must be upheld and what is happening now directly undermines that - New Zealand will be sending that message as strong as possible," Ardern said.
Mahuta said New Zealand had "consistently expressed our strong support for Ukraine's territorial integrity and sovereignty, and international diplomatic efforts to de-escalate the crisis to find a peaceful solution.
"A military invasion is an act of aggression, and a violation of one of the most basic tenets of international law. New Zealand is ready to take further measures," she said.
"We are very clear: any act of Russian aggression in Ukraine poses a direct threat to global peace and security, and would represent a further violation of international law," Mahuta said.
Mahuta said in the event of a full invasion, the Government was prepared to "respond with a suite of measures in line with those of our partners, and which will send a clear message of unity against an act of Russian aggression.
"These measures span the range of options available to New Zealand, including travel bans, controlled export bans and diplomatic measures".
The tools New Zealand has to respond to Russian aggression have become a political football in New Zealand with the opposition calling on the Government to pass autonomous sanctions legislation to give it greater sanctioning powers.
Ardern defended the lack of autonomous sanctions regime, saying things like "travel bans, export controls, [and] diplomatic measures" could be used to make New Zealand's feelings known to Russia.
