A senior Chinese diplomat has urged Myanmar to "cooperate" in maintaining stability on their shared border, Beijing said Monday, after armed groups fighting the junta seized a strategic trading outpost.

Assistant Foreign Minister Nong Rong visited Myanmar from Friday to Sunday, Beijing said, holding talks with senior junta officials on clashes the UN said have forced 23,000 people from their homes.

"Myanmar is called on to cooperate with China in maintaining stability along the China-Myanmar border," said Nong, according to a readout from China's foreign ministry.

Nong met with Deputy Prime Minister and Foreign Minister Than Shwe and Deputy Foreign Minister Lwin Oo during his visit, Beijing said.

China also urged the junta to "earnestly ensure the safety of the lives and property of Chinese border area residents, and take effective measures to strengthen the security of Chinese personnel, institutions and projects in Myanmar", he added.

Recent attacks, launched by an alliance of Myanmar ethnic minority groups in the northeast Shan state, represent the biggest military challenge faced by the junta since it seized power in 2021, analysts have said. 

Last week China called for an immediate ceasefire in the region, where a billion-dollar rail route — part of Beijing's global Belt and Road infrastructure project — is planned.

The junta on Saturday said the Kachin Independence Army (KIA), an ethnic armed group based in neighbouring Kachin state, had joined the attacks on its forces, promising retaliation.

Local media reported the junta had shelled the remote town of Laiza on the Chinese border, home to the KIA's headquarters.