A gunman has shot dead three police officers and the driver of an emergency rescue vehicle in Austria before barricading himself inside a farm building.

Interior Minister spokesman Karl-Heinz Grundboeck said initially the third policeman had been missing and presumed to be taken hostage, but his body was then found in his patrol car.

The gunman was barricaded in a building outside the Lower Austrian town of Melk, 40 miles from Vienna. The shootings happened overnight in the nearby town of Annaberg.

SWAT teams blocked off the area but police have not been able to establish contact with the gunman, reportedly a a 55-year-old poacher.

Mr Grundboeck said the man fled in a car when approached by police, then shot a member of Austria's Cobra SWAT team after his vehicle landed in a ditch.

He shot and killed the emergency driver as the man was administering first aid to the wounded policeman, and then shot and killed the second police officer at a roadblock before barricading himself in the building.