The trip is designed to underscore Washington's willingness to defend NATO allies, as fears rise that the month-old war in Ukraine could yet spark what Biden has called "World War III".
Fearing further escalation, cautious European Union, NATO and G7 leaders in Brussels shied away from Ukraine's request for more advanced weapons systems and a blanket embargo on Russian oil and gas at a trio of Brussels summits Thursday.
That prompted Ukrainian President Volodymyr Zelensky to pointedly question whether some allies -- particularly those in Europe -- were doing enough, quickly enough.
"You have applied sanctions. We are grateful. These are powerful steps. But it was a little late," he told EU leaders via video link, suggesting the invasion and untold bloodshed could have been prevented.
With his calls for fighter jets, missile defence systems, tanks, armoured vehicles and anti-ship missiles seemingly stalled, he warned Europeans about the cost of further delay.
Naming each EU member state in turn, he thanked countries including Poland and Estonia for their support, noted German backing came "a little later" and singled Hungary out for censure.
"You have to decide for yourself who you are with," Zelensky told Hungary's rightwing populist leader Viktor Orban, who has close ties to Moscow.
Zelensky said more weapons and more pressure on Moscow were urgently needed to help besieged Ukrainian cities.
"Listen, Viktor, do you know what's going on in Mariupol?" he said. "There is no time to hesitate. It's time to decide already."
Some in the West fear transferring ever-more lethal weapons to Ukraine could spark further escalation from Moscow that might prove cataclysmic.
Russia is already accused of using phosphorus bombs and indiscriminate shelling of civilian areas -- something the United States has branded a war crime.
And the Kremlin has pointedly refused to rule out using nuclear weapons, while producing a steady flow of disinformation about chemical and biological weapons that Washington says could be used as cover for their deployment by Moscow.
NATO leaders on Thursday decided to bolster their chemical and nuclear defences and announced the deployment of further troops to Romania, Hungary, Slovakia and Bulgaria in case Russia expands its attack beyond Ukraine.
In Poland, Biden will meet members of the US 82nd Airborne Division, part of NATO's increasingly muscular deployment to its eastern flank.
He will also receive a briefing on the dire humanitarian situation in Ukraine, which has seen more than 3.5 million people pour out of the country, mostly to Poland.
The UN believes that more than half of Ukraine's children have already been driven from their homes, "a grim milestone that could have lasting consequences for generations to come", according to Unicef chief Catherine Russell.
"Every day it's 20, 30 times we go to the basement (to shelter)," said a sobbing 37-year-old Vasiliy Kravchuk in the garrison town of Zhytomyr.
"It's difficult because my wife is pregnant, I have a little son."
While Ukrainian forces have stalled the initial Russian invasion and even launched some successful counterattacks, there are early signs that both sides are digging in for a long and bloody war that neither can easily win.
"It is obvious that the operation will continue until the objectives set by the president of the country are achieved," former president and top security official Dmitry Medvedev told Russian state news agency RIA Novosti.
In Mariupol about 100,000 civilians are said to be trapped in the southern port city with dwindling supplies of food, water and power, and with encircling Russian forces slowly grinding the city to dust.
Russia's highly censored media has broadcast aerial footage that appeared to be from Mariupol, showing a hellscape of charred and pocked apartment blocks spread across a singed and blackened wasteland.
Presenters blamed the devastation on Ukrainian "nationalists".
The city is a treasured prize for Russia as it would enable a land bridge between Russian-annexed Crimea and regions already controlled by Russian proxy forces in eastern Ukraine.
Kremlin-allied Chechen warlord Ramzan Kadyrov on Thursday claimed his forces had pierced Ukrainian defences to take Mariupol's city hall and hoist Russia's flag.
That claim was not verified, and Ukraine's armed forces said Russia was still trying to sack Mariupol "without success".
While some civilians have been able to flee to Ukrainian-controlled territory, local officials said as many as 15,000 Mariupol residents have been forcibly deported to Russia.
In recent days Ukraine has also shown its ability to go on the counter-attack, seemingly pushing Russia's military out of some towns near Kyiv and hitting valuable Russian targets in the south.
Ukraine on Friday claimed it had destroyed or damaged a small flotilla of Russian warships in the port city of Berdyansk.
According to the Ukrainian armed forces, Russian landing ship the "Saratov" was destroyed, and the landing ships "Caesar Kunikov" and "Novocherkassk" were damaged.
Images from the scene showed a large Russian warship ablaze at dockside, with other vessels steaming away from the inferno.
British military intelligence said the attack on "high-value" targets also destroyed an ammunition storage depot and was part of a broader strategy of Ukraine targeting vulnerable Russian supply lines.
"Ukrainians will continue to target logistical assets in Russian-held areas," the UK Ministry of Defence said.
"This will force the Russian military to prioritise the defence of their supply chain and deprive them of much-needed resupply for forces."
But it is far from clear that Ukraine can push the Russian forces out.
For now, the West seems content to squeeze Russia's economy and Putin's inner circle.
The European Union and the G7, also meeting in Brussels on Wednesday, pledged to block transactions involving the Russian central bank's gold reserves, to hamper any Moscow bid to circumvent Western sanctions.
And a series of countries announced asset freezes and travel bans on more Kremlin-connected individuals.
There was no agreement to halt oil and gas imports from Russia, which fill Moscow's war chest to the tune of hundreds of millions of dollars per day.