Earlier in the day, Xi arrived in Poland to meet the country's leadership and discuss economic cooperation and ties in such spheres as education, infrastructure and culture.
"The presidents of Poland and China, Andrzej Duda and Xi Jinping, in Warsaw on Monday signed a declaration on strategic partnership in which they reiterated that Poland and China viewed each other as long-term and stable strategic partners," the statement said.
According to the statement, the sides agreed to enhance cooperation in transport and logistics, civil aviation, agriculture and commerce, as well as environmental protection.
The sides also declared cooperation activities within the framework of the Polish Plan for Responsible Development and China's Silk Road Economic Belt.