Hillary Clinton’s meeting with 16 heads of state at the East Asia summit in Vietnam on Saturday was supposed to be a powerful signal of the renewed engagement of the US with the region.

But on her arrival in Hanoi, the US secretary of state found herself in the midst of a flare-up in smouldering Sino-Japanese relations that eclipsed the rest of the summit. One western diplomat described China’s acrimonious outburst and last-minute cancellation of a formal meeting between the Japanese and Chinese prime ministers as an “ambush” that took Japanese diplomats completely by surprise.

Wen Jiabao, China’s premier, and Naoto Kan, the Japanese prime minister, did get together for a very brief “unofficial meeting” away from the cameras on Saturday. But that was only after Beijing had sent a strong message by cancelling what would have been the first official meeting between the two leaders since a spat that began in early September when Japan detained a Chinese fishing boat captain in disputed waters.