He made the statement during a news conference in Warsaw after a meeting with European Council President Charles Michel.
The two met in the Polish capital to discuss a growing migrant and humanitarian crisis as Poland's eastern border remained under pressure from migrants arriving in Belarus from the Middle East and other countries outside Europe.
"The events of recent days represent a test for Poland and a test for Europe," Morawiecki told reporters, as quoted by the state PAP news agency.
"We realise the situation may get worse as Belarusian President Alexander Lukashenko and his principals employ ever new methods of provocation," he added.
"From a distance, the events taking place on the Polish-Belarusian border may look like a migrant crisis, but it is in fact a political crisis, designed to destabilise the European Union," Morawiecki told reporters.
Morawiecki said the circumstances called for "a shared response with the EU," adding that Michel was "fully aware of this necessity."
He told reporters that the EU should block flights to Belarus from the Middle East to stem the flow of
migrants seeking to enter the EU through its eastern external border.
"Today, we must step up our pressure through adequate sanctions, to make the Belarus regime stop" sending migrants across the EU frontier, Morawiecki said, as quoted by PAP.
'Case of state terrorism'
He told the news conference: "What we are dealing with on the Polish-Belarusian border is a case of state terrorism as well as Alexander Lukashenko's quiet revenge for our support for the Belarusian people and democracy during last year's elections."
"Today we are defending the Polish-Belarusian border, but we are also protecting NATO's eastern flank and the eastern border of the EU, because obviously Alexander Lukashenko is seeking to destabilise the whole of Europe," Morawiecki said.
"I am glad that the entire European Union and NATO are speaking with one voice," he added.
'Solidarity with Poland'
Meanwhile, Michel said he had come to Warsaw "to express the European Union's solidarity with Poland."
He described Belarus's policies as a "hybrid, brutal, violent and shameful attack," the PAP news agency reported.
"In the face of such a hybrid assault, we must act firmly together," he added, as quoted by the Polish state news agency.
Michel vowed that the European Council, the European Commission and member countries would consider "in the upcoming days" what action they could take to have a "significant and concrete" impact on the current situation.
He said one of the options was financing the construction of physical border infrastructure in "frontline countries," whose national frontiers are also the external borders of the EU, PAP reported.
The European Council represents the bloc's member states, while the Commission is the bloc's executive body.
Poland's Morawiecki told lawmakers on Tuesday that the migrant crisis was the most serious security risk facing Poland in decades, the news agency said. The PM also said the crisis was being masterminded by Russia's leader Vladimir Putin.
Polish border guards, police and soldiers on Monday thwarted several attempts by migrants to force their way into the country via Belarus, with fresh thrusts taking place early Wednesday, government officials said, as the border crisis escalated.
EU, NATO, US condemn Belarus
The United States on Monday voiced concern over "disturbing images and reports" from the Polish-Belarusian border, and condemned Belarus for "orchestrating" migrants flows to Europe.
NATO condemned the use of migrants by Belarus "as a hybrid tactic," with its Secretary-General Jens Stoltenberg voicing solidarity with Poland amid the border standoff.
Meanwhile, European Commission head Ursula von der Leyen called for EU member states to approve new sanctions against Belarus, which she said was responsible for a "hybrid attack" on the Polish border using migrants.
The European Union has accused Belarus of encouraging thousands of migrants from the Middle East and Africa to cross into EU countries via Belarus, as a form of hybrid warfare in revenge for Western sanctions on Minsk over human rights abuses, the Reuters news agency reported.
Poland and the Baltic states have accused Belarus's strongman leader Alexander Lukashenko of organising a wave of illegal migrants seeking to enter the bloc as part of what officials have called a "hybrid war."
The EU Commissioner for Home Affairs, Ylva Johansson, visited Poland in late September, agreeing with Warsaw’s arguments that “firm steps” were needed against Belarus, according to officials.
Poland's Morawiecki said last month that his country enjoyed full support within the European Union as it worked to defend itself against a migrant influx and a "hybrid war" being waged by Belarus.
In late September, Polish lawmakers voted overwhelmingly to extend a state of emergency in parts of two regions along the country's eastern border with Belarus by two months amid a growing migrant surge.
The state of emergency gives authorities broader powers to monitor and control the movement of people on the Polish-Belarusian border, which is also the eastern border of the European Union.