The Health Secretary warned the Kremlin this morning that there would be a “significant response” to any aggression.
Russia launched missile strikes just 12 miles from the Polish border with Ukraine last night, raising fears of a new global conflict.
Warsaw is part of the 30-strong defensive military alliance which also includes the UK, US, France, and Germany.
Mr Javid said: “We’ve been very clear from the start, with our NATO allies, that if there is any kind of attack on NATO territory then it will be war with NATO and there will be a severe response.
“Even if just a single toecap of a Russian soldier steps into NATO territory, then it will be war with Russia and NATO would respond”.
Last night Russian forces fired more than 30 cruise missiles at the Yavoriv military base near Lviv in the west of Ukraine.
The strike on the base, where foreign instructors were helping Ukrainians, killed at least 35 people and injured 134.
People living on the Polish side of the border could clearly see the explosions lighting up the sky.
Last week armed forces minister James Heappey, a former Army major, said Putin would be desperate to avoid war with NATO.
He said the Alliance would “completely overmatch the Russian military both in terms of technology and mass”.
NATO allies including Britain and the US have massively bolstered deployments to Eastern Europe in recent months.
Mr Javid also said the Russian army’s bombing of hospitals “fills me with rage” and amounts to “war crimes”.
He added: “It’s appalling atrocities. Putin will be ultimately held responsible for sure by the International Court.”
Today it emerged that a pregnant mum and her unborn baby died after a Russian airstrike hit a maternity ward.
His remarks come amid a ratcheting up of tensions as Kremlin forces become increasingly desperate to break Ukrainian resistance.
Russia has lost more than 12,000 troops during almost three weeks of fighting as well as hundreds of tanks and aircraft, according to Ukrainian estimates.
There have been widespread reports that morale is incredibly low, with kit repeatedly breaking down and shortages of food and fuel.
Putin has even resorted to calling in mercenaries from as far afield as Syria to bolster his struggling forces.
Moscow is becoming so desperate it has even asked China for help.
US National Security Adviser Jake Sullivan warned Beijing would “absolutely” face consequences if it offered Russia support.
So far China has failed to endorse Russia’s invasion of Ukraine, but it has refused to outright condemn it either.