Former prime minister Jim Bolger is fearful Russian President Vladimir Putin will try to invade other former Soviet states after Ukraine, in an attempt to restore the Soviet Union.
Bolger, who was prime minister as the Soviet Union fell in 1991, said the Russian invasion of Ukraine was a disaster, and these were "frightening days".
Bolger said Putin was likely emboldened by Russia's annexation of the Crimea Peninsula in 2014.
"I surmise from his perspective that didn't cost him much, so he's trying again," Bolger said.
"I wouldn't be at all surprised if his ambition was to try recreate the old Soviet Empire. Of course that means a number of other much smaller republics than the Ukraine must be fearful of what Putin might decide to do on their borders. This is what makes this so dangerous.
"If this naked attempt to take over another country is successful, why would Putin stop there?"
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- NZ announces bans on Russia in response to Ukraine invasion
Bolger said the West should try restrict economic activity and freedom for Putin and his supporters.
"The aim has to be to inflict punishment, penalties, on Putin and his oligarch friends, many of whom live in the West - I don't know whether any still live in New Zealand - so they don't gain anything.
"Sanctions are the step that, if taken with enough rigour, that will have an impact. I surmise that those who are supporting Mr Putin at the moment are just watching to see how rigorous the West will be in imposing sanctions, and how many will be worried about the impact on their own economies."
Bolger said he agreed with Prime Minister Jacinda Ardern that New Zealand strongly condemn Russia's actions and align with Western allies.