"It is a gesture of solidarity and support for our neighbour and ally," the Polish foreign ministry said.
The convoy, organised by Poland’s Government Strategic Reserves Agency, arrived in Vilnius carrying tents, power generators, blankets and camp beds worth about PLN 740,000 (EUR 162,000) in total, public broadcaster Polish Radio reported.
The problem of illegal migrants trying to reach western Europe through Lithuania has recently worsened, according to officials.
This year, the Lithuanian-Belarusian border has been illegally crossed by at least 1,800 people arriving mainly from Iraq, Syria, Tajikistan and Russia, according to Lithuania's State Border Guard Service, Poland’s PAP news agency has reported.
Last year, the number of illegal crossers totalled 74, up from 37 in 2019.
In an effort to contain the growing inflow of illegal migrants from Belarus, Lithuania declared a state of emergency on July 2.
Lithuania’s Interior Minister Agnė Bilotaitė has said the surge in migrants this year has been "a form of hybrid warfare" in which the Belarusian government is involved, the Polish news agency reported.
"We declare full solidarity with Lithuania and we appeal to all European Union countries to support the authorities in Vilnius in their efforts to secure the EU's external border," the Polish foreign ministry said in a statement.
Poland's Foreign Minister Zbigniew Rau, who visited Vilnius earlier this month, said the growing migrant numbers posed a problem not only for Lithuania, but the whole of the European Union.
Meanwhile, Poland's defence ministry is putting together another convoy of humanitarian aid amid the migration crisis in Lithuania, officials announced.