A gunman went on a deadly rampage in an Amish schoolhouse today, shooting dead three girls "execution style" and shattering the calm inside one of America’s most reclusive and pacifist communities.

The gunman, a truck driver identified as Charles Carl Roberts IV, 32, entered Wolf Rock School in Paradise, Pennsylvania, just after 10.30am brandishing a handgun and automatic shotgun.

He let the 15 boys go from the one-room school, as well as one pregnant woman and three women with young infants, but took all the remaining girls hostage.

Seven other girls were wounded, some critically. Three girls aged from 6 to 15 have been admitted to local hospitals with gunshot wounds and all were in a critical condition.

Commissioner Jeffrey Miller, of the Pennsylvania police, said that the attack took place as "revenge" for an episode in the gunman’s life that took place 20 years ago.

"From what we know at this point it seem he wanted to attack young female victims. The girls were shot execution-style in the head," he said. "There was some issue in the past which for some reason meant he wanted to extract revenge against female victims."

Roberts used both guns in tandem to carry out the killings. Mr Miller said that during the attack, Roberts apparently told students to line up in front of the blackboard. He began to tie his female captives' feet together. Then he let the boys in the classroom leave.

Commissioner Miller said Roberts, who lived very near the school, left a "rambling" suicide note.

He added that Roberts called his wife while he was inside the school. She said he didn't know where he was, but that he couldn't go on any more and he was getting revenge for something that happened 20 years ago.

The officer said he targeted the school because it provided him with a "close opportunity to attack where he knew there would be young kids".

It was the nation’s third deadly school shooting in less than a week, and one of the deadliest in American history. Police said Roberts was not a member of the Amish community and that the attack was unrelated to it. "It’s a horrendous crime scene," Mr Miller said. "One of the victims died in a trooper's arms."

The tragedy left the Amish community in the Pennsylvania enclave of Paradise Township in deep shock, particularly as the Amish, notable for their horsedrawn buggies and traditional dress, reject the trappings of modern life, including cars, guns and telephones.

After the gunman — a father of three — took the hostages, police were notified of the incident at 10.36am.

By 10.45am, dozens of police and medical emergency teams had been dispatched to the scene and surrounded the school.

Negotiations took place for 45 minutes before the gunman called a local radio station on his mobile phone and said that if police did not leave within 10 seconds, he would open fire on the hostages.

"Within a matter of seconds, they heard shots, multiple shots," Mr Miller said. State troopers broke into the school and found the gunman dead.

The gunman, who police said was local and well-known in the community, worked as a milk tanker driver. After dropping his own children off at school at 8.45am this morning, he had returned home and left suicide notes to his family.

Police said today that there had been three fatalities, but the local coroner had earlier reported the death toll at six.

Officials at the Penn State Milton S Hershey Medical Centre confirmed that other victims were also being admitted there.

According to a witness, a man in a pick-up truck pulled up outside the school, before running into the building. He ordered all the boys to leave the room, and took the remaining girls hostage. A teacher and some visitors fled and ran to a nearby farm.

He barricaded himself inside, blocking the doors using timber he had brought himself. Police had to smash windows to break their way in.

The schoolhouse formed the heart of the community, a heavily settled Amish area just outside the town of Nickel Mines, about 55 miles west of Philadelphia. It is surrounded by farmland and Dutch barns. About 30 children attended the school.

As news of the tragedy spread, many Amish men, with their trademark beards and broad-brimmed black hats, could be seen spreading out through the fields searching for children who are believed to have fled the schoolhouse during the shooting.

Most traditional Amish are members of the Old Order Amish Mennonite Church.

They are best known for their plain clothing, most of it self-made, essentially that of 17th-century German and Dutch peasants. Men grow beards after they marry but are forbidden to have moustaches. They shun modern life, including televisions and home-based telephones, and the Old Order Amish even refuse to operate farm machinery.

"This would have been shocking to the children," said Professor Donald Kraybill, an expert on the Amish community. "They wouldn't have been exposed to any of this on television."

Nearly all Amish schools are located in rural areas, and are usually one-room buildings operated by Amish parents, reflecting the close-knit nature of their communities.

Although they shun modern life, they have been forced to live amid it. Many Amish communities in Lancaster county, where today's shooting took place, are only a few hundred yards from highways and shopping malls, and their horse and buggies can frequently be seen negotiating traffic.

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