A policeman was rushed to a hospital with a suspected fractured skull after being "hit by an object," officials said.
Six other officers, including one policewoman, suffered less serious injuries after being hit by rocks and other objects thrown from across the border, according to the Polish police force.
Meanwhile, a female border guard and a soldier were also hurt in the border clashes, state news agency PAP reported.
The "migrant attack" was mostly staged by "young, aggressive men," the Polish defence ministry tweeted.
Migrant pressure
The incidents came amid turmoil on Poland's eastern border with Belarus, with thousands of migrants seeking to cross illegally into the country, and thus the European Union.
Poland, the EU and its member states, as well as NATO and the United States have accused Belarus's autocratic leader Alexander Lukashenko of orchestrating the standoff in retaliation for Western sanctions against his regime.
The EU agreed on Monday to step up sanctions against Belarus, which it says is pushing migrants toward the bloc in revenge for earlier sanctions over a crackdown on protests last year against strongman leader Alexander Lukashenko's contested re-election, the Reuters news agency reported.
Lukashenko has denied luring vulnerable people, including Kurds from the Middle East, with the false promise of easy access to the EU and sending them over the bloc's border.
'Aggressive migrants throwing stones at our soldiers'
Also on Monday, thousands of migrants were escorted by Belarusian security forces towards a closed border crossing at Kuźnica, according to Polish officials.
On Tuesday morning, the Polish defence ministry tweeted a series of short videos that it said showed migrants attacking Polish soldiers and officers with stones and trying to destroy the border fence to get into the country.
"Our services used tear gas to stifle the aggression of migrants," the Polish defence ministry said.
In another video posted on Twitter, the Polish defence ministry said that migrants attacking Polish soldiers and police officers were using stun grenades handed to them "by the Belarusian services."
'Hard day for Polish officers and soldiers'
A spokesman for Poland's security services, Stanisław Żaryn, tweeted on Tuesday evening: "Hard day for Polish officers and soldiers who stand watch over Poland's state border. Today migrants, controlled by Belarusian services, have launched an unprecedented attack."
In an earlier tweet, Żaryn said that "a massive attack on the Polish border with Belarus has been repelled."
He added that "organized, mob-style violence will only make the Poles more determined to protect the Polish and EU border."
Poland's Border Guard on Tuesday said it had recorded 224 illegal attempts to cross from Belarus over the past 24 hours. Since the start of the year, over 33,000 such attempts have been recorded, the PAP news agency reported.
Since September 2, Warsaw has kept the border zone under a state of emergency in the face of the migrant pressure.
Poland also plans to build a solid fence along the Belarus frontier, crowned with barbed wire and fitted with electronic surveillance devices. The protective wall is due to be ready by mid-2022.
EU, NATO, US, UN nations condemn Belarus
The United States has called on Russia to use its influence over Belarus "to cease its callous exploitation and coercion of vulnerable people," White House spokeswoman Jen Psaki said on Monday amid the deepening migrant crisis on the Polish-Belarusian border.
US State Secretary Antony Blinken at the weekend reaffirmed America's support for Poland amid the crisis on the EU member's border with Belarus.
The United States and European members of the UN Security Council last week condemned Belarus for the “orchestrated instrumentalization" of migrants as tensions rose along the Polish-Belarusian border.
The Polish prime minister has said that NATO must take steps to help resolve the crisis on the Belarus border, adding that Poland and the Baltic states of Lithuania and Latvia may ask for consultations under Article 4 of the alliance's treaty.
Polish lawmakers were on Tuesday set to debate legislation to strengthen the country's frontiers amid rising tensions on the border with Belarus.
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Source: PAP, IAR