Nato Secretary General Mark Rutte has said that the military alliance will defend every inch of its territory as he asked Russian President Vladimir Putin to stop the violation of allied airspace.
Rutte also said that Russian drone incursion was "absolutely reckless" and that a full assessment of the incident had not yet been made.
"Whether it was intentionally or not, it is absolutely reckless, it is absolutely dangerous. But the full assessment is ongoing," Rutte said. "To Putin, my message is clear. Stop the war in Ukraine. Stop violating allied airspace. And know that we stand ready, that we are vigilant, and that we will defend every inch of Nato territory."
Germany said that the drone incursion in Poland is very serious and shows how much Russia is testing European resolve.
"It shows once again what a threat we are under and how much we are being tested by Russia," the German foreign minister said during a news conference.
"Russia has recklessly accepted a dangerous escalation," minister Johann Wadephul said at a news conference with his Dutch counterpart.
"..it is clear that even after three years, Moscow is still not prepared to negotiate seriously for peace…the Kremlin wants to subjugate Ukraine by force. We must and will respond to this with a clear answer," he added.
Poland said on early Wednesday that its airspace was violated by Russian drones, and that the country and its Nato allies shot down some that posed a direct threat.
“Last night the Polish airspace was violated by a huge number of Russian drones. Those drones that posed a direct threat were shot down,” Polish Prime Minister Donald Tusk wrote on social media.
Tusk told parliament it was "the closest we have been to open conflict since World War Two", although he also said he had "no reason to believe we're on the brink of war".
He further said he had activated Article 4 of Nato's treaty, under which alliance members can demand consultations with their allies.
Poland's armed forces were on a state of alert overnight Tuesday and early Wednesday because of what they described as “further massive airstrikes against targets located in Ukraine.”
Defence minister Wladyslaw Kosiniak-Kamysz wrote on X that “more than ten objects” crossed into Polish airspace, and those that constituted a risk to Poland's security were neutralised.
Warsaw's Chopin Airport suspended flights for several hours, citing the closure of airspace due to military operations.
The Polish armed forces said that a search for possible crash sites is ongoing and urged people not to approach, touch or move any objects they see, warning that they may pose a threat and could contain hazardous material.
Moscow has denied responsibility.
Russia's defence ministry said that its drones had attacked military facilities in western Ukraine but it had not planned to hit any targets in Poland.
The ministry said its forces had achieved all its targets in the attack, and pointed out that the Russian drones "which allegedly crossed the border with Poland" had a range of not more than 700 km (434 miles).
"Nevertheless, we are prepared to hold consultations with the Polish defence ministry on this topic," it said.
Kremlin spokesman Dmitry Peskov said that the Kremlin had not received any requests for contact from Poland, but dismissed European Union and Nato accusations that Russia had carried out a provocation.
"The leadership of the EU and Nato accuse Russia of provocations on a daily basis. Most of the time, without even trying to present at least some kind of argument," Peskov said.
Russia launched around 415 drones and over 40 missiles across 15 Ukrainian regions, Ukrainian President Volodymyr Zelenskyy said. Ukraine's air force reported shooting down 386 drones and 27 of the 43 missiles.
European leaders, who have been trying to persuade US President Donald Trump to join them in tightening sanctions on Russia and boosting support for Kyiv, said it justified a collective response.
There was no immediate response from Washington.
Poland has complained about Russian objects entering its airspace during attacks on Ukraine before.
In August, Poland's defence minister said that a flying object that crashed and exploded in a cornfield in eastern Poland was identified as a Russian drone, and called it a provocation by Russia.
In March, Poland scrambled jets after a Russian missile briefly passed through Polish airspace on its way to a target in western Ukraine, and in 2022, a missile that was likely fired by Ukraine to intercept a Russian attack landed in Poland, killing two people.