Poland, an EU and NATO member and ally of Ukraine, announced last week the closure of the frontier during military drills being conducted in Belarus by Russian and local troops.

The situation on the border is tense, with Poland accusing Russia of launching a recent incursion by military drones and Belarus of encouraging a wave of undocumented migrants.

But by imposing a halt on cross-border traffic, Poland has also blocked a rail line that is one of China's main overland trade routes into the European Union.

Polish foreign minister spokesman Pawel Wronski said Foreign Minister Radoslaw Sikorski had met China's top diplomat Wang Yi in Warsaw and briefed him on the situation.

"This is not a decision aimed at hitting anyone among the partners who transport goods," he said.

"Manoeuvres with a very aggressive scenario are currently taking place in Belarus," and Poland is continually exposed to a "hybrid war" on its eastern borders, the spokesman said.

"The logic of security prevails in our region over that of trade," he explained. "It is difficult to conduct free trade when a border is not a secure border."

Wang arrived in Poland on Monday after visiting Austria and Slovenia, amid deadlock in international diplomatic efforts to end the war in Ukraine.

China regularly calls for peace talks and respect for the territorial integrity of all countries, implicitly including Ukraine. Western powers would like Beijing to do more ro rein in Moscow.

But Beijing has never condemned Russia and has strengthened its trade, diplomatic and military ties with Moscow. China is accused by some of Kyiv's allies of helping its Russian neighbour bypass Western sanctions.