A four-year-old girl is dead and doctors are battling to save the life of her mother after the pair were found in a room full of charcoal smoke at their Tai Po home yesterday. Tang Pui-yan and So Yuet-kam, 33, were found at 4.30pm by father Tang Hung-chau, 46, who dashed home after receiving a call from a friend of his wife. Two trays of burning charcoal were on the floor. Ms So was in critical condition in Alice Ho Miu Ling Nethersole Hospital last night. Police said she called her friend about midday, saying she was going to kill herself, then hung up. The friend, 49, called her back but got no reply and rushed to their Tai Po home. When no one answered the door, she called Mr Tang at the Sheung Shui garage where he works. Friends said Ms So, an avid mahjong player, had been saying in recent days that she wanted to kill herself over her gambling debts, said to amount to more than $100,000. Detectives from Tai Po police station are investigating whether Ms So and her daughter had taken any pills or medicine before the charcoal was lit, turning the flat into a gas chamber. Ms So left a suicide note on a table saying 'there was nothing worth living for in the world', a police source said. Pui-yan was declared dead at the hospital at 5.30pm. 'It is possible that the woman will face a murder charge over the death of her daughter,' a police source said. Police said Mr Tang was saddened and shocked over the death of his daughter, the only child in his family. Last night, a police spokesman said the case had not been classified and no arrest had been made. Suicide hotline numbers: Samaritans (multi-lingual) 2896 0000, and Samaritan Befrienders (Cantonese) 2389 2222.