A Canadian visitor was walking on Beijing Road in Lhasa on Friday afternoon when he saw a crowd of Tibetans beating a young Han Chinese man and two women.
At first he watched, stunned, as the crowd, armed with sticks and metal clubs, beat the man, aged about 20, until he fell to the ground unconscious.
Then he recalled rioters in Paris beating him to the ground and leaving him with a dislocated shoulder.
'I told myself, 'I can't just let this guy die on the ground,' the man said yesterday by phone from Lhasa. 'I remembered what happened to me. I couldn't let that happen to somebody else.'
When he intervened, the Tibetans stopped their attack.
'The rioters had a lot of anger, but I don't think they actually wanted to kill anybody,' he said.
He lifted the man to his feet and helped him stumble towards a hospital. 'He must have passed out four times on the way to the hospital. As soon as he got in the door, he collapsed,' he said.