Morawiecki made the statement in a Facebook post as he attended a gathering of the National Security Council to discuss the migrant pressures, which have been mounting on the Polish-Belarusian border since the summer, the state PAP news agency reported.
The meeting had been called by President Andrzej Duda after a series of attempts by migrants to force their way into Poland from Belarus on Monday, according to officials.
Earlier in the day, Morawiecki led a crisis management team meeting that was also attended by Deputy Prime Minister Jarosław Kaczyński and the country's interior, defence and foreign ministers.
After the National Security Council meeting, government spokesman Piotr Müller told reporters that Poland's frontier was "under concerted attack" and that it would be strengthened.
He added that some 3,000 to 4,000 migrants had gathered at the border, while fresh transports kept arriving in Belarus "from Arab countries."
Meanwhile, the Baltic states of Lithuania, Latvia and Estonia expressed their solidarity as Poland faces growing migrant pressure on its eastern border, PAP reported.
Müller said the Polish prime minister was set to speak to his Lithuanian and Latvian counterparts by phone on Monday evening.
Polish border guards, police and soldiers on Monday thwarted several attempts by migrants to forcibly enter the country via Belarus, government officials said, as the border crisis escalated.
Belarusian opposition journalist Tadeusz Giczan tweeted that "the standoff continues" with some of the migrants using wire cutters and tree trunks to try and force their way across the border, and Polish officials warding them off, PAP 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 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.
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 Prime Minister Mateusz 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.
Source: PAP, tvp.info