Hong Kong's third critical case of H1N1 has been detected among the increased 1640 cases, involving a 39-year-old woman, the Hospital Authority (HA) said on Friday.

She came down with flu symptoms on July 9 and was treated at the centre on July 12 for upper respiratory tract infection and discharged. Without improvement, she was hospitalised July 13. She was diagnosed to have a chest infection and tested negative for swine flu July 14. However her condition worsened, requiring respiratory support early Friday. She is now getting Tamiflu treatment.

There were 88 new H1N1 cases confirmed on Friday involving 43 men and 45 women aged five to 64, bringing Hong Kong's tally to 1,640.

Currently, a total of 19 confirmed cases are staying in public hospitals for treatment. Among them, 13 cases are in stable condition, three in serious and three in critical condition.

The new cases involve a Queen Mary Hospital nurse and three men and three women aged 22 to 46 from a residential workshop for the physically and mentally disabled in Eastern District - four workshop attendees, a resident and a staff member.

The workshop was earlier reported to have a respiratory tract infection outbreak with a confirmed swine flu case affecting a 22-year-old man.