JAKARTA, June 23 (Reuters) - A 3-year-old Indonesian girl has tested positive for bird flu and is being treated in a hospital in Sumatra, a health ministry official said on Saturday.

The girl from the town of Rumbai in Riau Province fell sick on Wednesday and was being treated at the Arifin Achmad hospital in Pakanbaru, said Joko Suyono at the ministry"e;s bird flu centre.

"She tested positively for bird flu in two laboratory tests," Suyono said, adding that she had been in contact with dead chickens. The official said her condition was improving, although did not elaborate.

There have now been 101 confirmed human cases and 80 deaths in Indonesia, the highest in the world.

While bird flu is mainly an animal disease, experts fear it could mutate into a form that can be spread easily among people, triggering a possible pandemic which could kill millions.

Globally, there have been 314 cases including the latest one and 191 deaths, according to World Health Organisation data.

Indonesian Health Minister Siti Fadillah Supari said on Friday that a vaccine to combat human bird flu could be ready as early as next month and it was prepared to use it immediately despite calls from the WHO to build up a stockpile first.

The minister said clinical trials should wrap up soon for the vaccine, which is being jointly developed with a unit of U.S. firm Baxter International Inc.

The Indonesian government and Baxter agreed in February to develop a vaccine. Under the agreement, Indonesia has been supplying virus specimens, while Baxter is providing the technology to develop the vaccine.