I think they will act if this stretches into a lengthy engagement. They want to see the US solidly committed.

They are helping Iran militarily and diplomatically. The last attack on Iran ended in 12 days. The Americans or Israelis haven't send any boots as a proper invasion requires. So they are just waiting and watching.

China is starting to act.[1][2] There's a summit with Xi and Trump coming up. China is pushing for a cease fire with Iran. China has also stopped aggressive flights over Taiwan airspace for the last week, for whatever reason.

Diplomats on the China side are worried about the Trump administrations's amateurish approach to diplomacy. "... Trump’s reluctance to delegate, disdain for process and focus on quick wins, banking instead on personal magnetism and his “gut” as summit organising principles. ... “You have a handful of people who have never done this before, putting together what may be the most consequential trip in the president’s administration on a wing and a prayer. The Chinese are beyond worried. They’re apoplectic.” - South China Morning Post.

[1] https://www.cnn.com/2026/03/07/china/china-us-iran-wang-yi-i...

[2] https://www.scmp.com/topics/2026-trump-xi-summit

[3] https://www.scmp.com/news/china/article/3344769/trump-xi-sum...

[4] https://www.scmp.com/news/china/article/3344769/trump-xi-sum...