A doctor in Brazil has been charged with the murder of seven patients, and authorities are investigating the possibility she is responsible for around 300 more deaths to free up hospital beds.

Virginia Soares de Souza is accused of cutting off patients' life support machines and administrating lethal doses of muscle-relaxing drugs at the Evangelica Hospital of Curitiba.

Having originally been accused of intentionally killing seven people, the number of Souza's potential victims sored after investigators began checking the patients who have died in her care over the last seven years.

Souza was arrested in February along with three doctors and a nurse who are suspected of conspiracy.

If the numbers are confirmed, Souza would overtake Dr Harold Shipman as the world's most prolific serial killer. The GP was convicted in 2000 of killing 15 patients in Manchester and was later found to have killed between 215 and 260 over a 23-year-period.

Dr Mario Lobato, lead investigator, said he has already closed the book on 20 cases and is now looking into around 300 more.

He told Brazil's Fantastico TV program: "All of them have the same modus operando, the same relationship between the drug and death, and the same time between both."

Lobato added that in some of the cases, the patients were conscious and talking before they died.

"One was awake, being nebulised but not even connected to a respirator.

"This patient had asked his family to bring his glasses so he could do some reading while he was in the intensive care ward. Another patient had just asked a nurse for a cup of water.

"This nurse testified that one of the things she will never forget is that she didn't manage to give him the cup of water because by the time she returned he had already died."

Souza's lawyer, Elias Mattar, said her client will be denying the charges. He said: "We will soon prove that everything that happened in that ICU was justified by medical procedure."

All the suspects in the case have been released on bail.