Chinese state media and netizens alike have joined the government in condemning Japanese Prime Minister Shinzo Abe's visit to the Yasukuni war shrine, with analysts predicting a more robust response to come from China.
Emotions also ran high in South Korea, whose ties with Japan have already been testy over various issues, and security around the Japanese embassy in Seoul was beefed up in anticipation of incidents today.
China's official Xinhua news agency, in one of two commentaries released hours after Mr Abe's visit on Thursday, called it "a grave provocation that may lead to heightened tension in the region".
"Choosing a sensitive time to visit a highly controversial and notorious place, Abe knows perfectly what he is doing and the consequences," wrote Xinhua.
China's Internet users were peeved that Mr Abe chose to visit the shrine on the day Chinese leaders like President Xi Jinping were attending public events marking the 120th birth anniversary of late strongman Mao Zedong.
One user said the shrine visit signals Mr Abe's aim to remilitarise Japan and invade countries like in World War II, saying: "If we are not aware of this possibility, our future generations could one day become war slaves."
Observers say China is set to unleash greater anger, compared with its restrained reaction the last time a serving Japanese premier visited the shrine.
Mr Junichiro Koizumi did so in 2006 shortly before stepping down, but Beijing reportedly reined in public sentiment then to focus on a post-Koizumi era.
But there are new factors now, such as the Japanese government's nationalisation in September last year of some of the Diaoyu/Senkaku islands, to which both sides have claims.
Also, China could be more motivated to castigate Mr Abe's visit, which it views as more damaging than Mr Koizumi's in 2006 - though the latter had done so on Aug 15, a sensitive date marking Japan's surrender in World War II.