Hong Kong counsellors went undercover among Japan quake survivors to discover how they had been affected by the ordeal.
Timothy To Wing-ching, executive director of the Post Crisis Counselling Network, said helpers were warned that people in northeast Japan - the area worst-hit by the disaster - were quite shy.
So instead of approaching them directly, they tried to win their confidence by other means before starting the real work of identifying those suffering from post-traumatic stress disorder.
'We pretended we needed their help,' To said. 'Volunteers jogged near their shelter in the hope of meeting them, and sometimes asked where the toilet was or what a Japanese word meant.'
Of 99 survivors the team assessed at a hotel used as a temporary shelter in the city of Hanamaki in Iwate prefecture, about a third had the disorder, which can cause sleeplessness and delusions.
Most of the people they met were elderly fishing people or farmers.
Some of the traumatised survivors were suicidal, while others were convinced another earthquake was occurring and said they felt the ground shaking when it was not.
To, who went to Sichuan and South Asia after previous disasters, said one of the big differences he found in Japan was the polarised emotional response to the tragedy.
Some survivors seemed to be coping well while others were deeply troubled.
'A lady burst into tears when I talked about Hong Kong people's love for sashimi. She was a fisherwoman in her 60s and used to have sashimi every day. It's a part of her life,' he said.
The team will organise a fund-raising concert next month to fund another 20 trips to Japan.