Victims' blood 'is lifesaver'.
Doctors there gave blood plasma from other H1N1 patients to victims fighting for life in intensive care.
And only a fifth of patients given the plasma died, compared to more than half of a "control" group who did not receive the blood product.
The blood of swine flu survivors contains antibodies which help others fight the H1N1 virus, and these antibodies can be passed to other patients.
The Hong Kong researchers, whose findings are reported in the journal Clinical Infectious Diseases, wrote: "This study has demonstrated that convalescent plasma treatment may have a place in the treatment of patients with severe H1N1 infection."
The scientists say flu does not build up a resistance to blood plasma antibodies, like it does with some drugs.
And they believe plasma treatment could also help victims of future flu strains.
Plasma, a yellowish liquid, is effectively blood which has had the red and white blood cells stripped out.