A Brazilian doctor, on trial for killing seven patients in order to free up hospital beds, could be responsible for more than three hundred deaths health authorities have said.

In what could be one of the world's worst serial killings, Virginia Soares de Souza is accused of administering fatal doses of muscle-relaxing drugs, and reducing the amount of oxygen to people on life-support machines at the Evangelica Hospital of Curitiba.

De Souza, who was arrested last month following the premature deaths of a number of terminally ill patients, has been initially charged with involvement in the deaths of seven patients.

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Dr Mario Lobato, who is leading the investigation, told Brazil's Fantastico TV programme that De Souza had 'played God' in deciding which of the patients should die in order to free up beds in the hospital.

According to the Daily Mail he told the television programme: "There are 20 cases which have already been closed, and we have nearly 300 cases still open which we are looking at.

"In each case, the testimony of people who worked inside the hospital confirmed what we have found on the patient records."

Lobato is quoted as saying that in one case the patient asked a nurse for a cup of water and by the time she had returned the patient was dead.

De Souza, who was also a director of the hospital in the east of the country, was arrested in February along with three doctors and a nurse.

Three other members of staff have also subsequently been charged in the case.

De Souza's lawyer, Elias Mattar Assad, said she would prove her innocence.

The case has been compared to that of British doctor Harold Shipman who was responsible for the deaths of at least 215 patients over a 25 year period.

If the death toll of more than three hundred people is correct it would implicate De Souza in one of the world's worst serial killings.