China is concerned about recent clashes between Pakistan and Afghanistan and has asked the two countries to protect its nationals and investments in the region, Beijing's foreign ministry said on Monday.

Dozens of fighters were killed in overnight border clashes between Pakistan and Afghanistan, both sides said on Sunday, in the most serious fighting between the neighbours since the Taliban came to power in Kabul.

China shares a border with Afghanistan and Pakistan in its western region and has sought to play a mediating role in calming hostilities between the two sides, who were allies until recently.

"China is willing to continue to play a constructive role in improving and developing Pakistan-Afghanistan relations," foreign ministry spokesperson Lin Jian said during a regular press briefing.

Also Read: Pak-Afghan border closed for second day amid escalating tensions

Beijing hopes that Kabul and Islamabad will "remain calm and restrained, and persist in properly resolving each other's concerns through dialogue and consultation to avoid escalation of conflicts," Lin said.

In August, China's Foreign Minister Wang Yi attended a meeting with Pakistani and Afghan counterparts in Kabul, calling for strengthening exchanges at all levels.

In an informal trilateral meeting weeks earlier, hosted by Beijing, China said Kabul and Islamabad had agreed to upgrade their diplomatic ties.