China on Wednesday expressed regret and concern over Indian strikes on Pakistan, urging both sides to show restraint in response to a major escalation between its nuclear-armed neighbours.

India and Pakistan exchanged heavy artillery fire along their contested frontier on Wednesday, after New Delhi launched missile strikes on its arch-rival.

Pakistan said Indian strikes had killed at least 26 people, and India said Pakistani artillery fire had killed at least eight along the de facto border in contested Kashmir.

China, which shares land borders with both countries and is a close ally of Pakistan, said it expressed "regret over India's military action this morning" and said it was "concerned about the current developments".

"India and Pakistan are neighbours that cannot be moved apart, and they are also China's neighbours," a foreign ministry spokesperson said in a statement.

"China opposes all forms of terrorism," they said.

"We call on both India and Pakistan to prioritise peace and stability, remain calm and restrained and avoid taking actions that further complicate the situation," the spokesperson added.

At a briefing on Wednesday, Beijing also offered to play a mediating role in reducing tensions.

"We are willing to work together with the international community and continue to play a constructive role in easing the current tensions," foreign ministry spokesman Lin Jian said.