Three people died Tuesday in a fire at a hospital just south of Austria's capital, a spokeswoman said.

"The cause of the fire could not yet be determined with certainty," said the spokeswoman for the hospital in Modling, about 14 kilometres from Vienna.

The fire broke out at the hospital at around 1am local time (2300 GMT on Monday), according to a statement from the regional health agency.

Authorities said 33 vehicles, 170 firefighters and a Red Cross team were dispatched to put out the blaze, which was brought under control after two hours.

Uninjured patients were transferred to other facilities and an investigation has been launched, they said.