Investigation underway into whether car's handbrake was deactivated.

The mayor of L'Aquila in Italy's central Abruzzo region has declared a period of mourning after a tragic incident in which a four-year-old boy died and five others were seriously injured when a car, minus its driver, ploughed into a nursery playground.

According to Italian media reports, the owner of the car had left her son - aged 12 - in the vehicle unattended while she collected her five-year-old twins from the school in the city's Pile suburb at around 14.30 on Wednesday afternoon, reports news agency ANSA.

The car - a Volkswagen Passat - then rolled down the hill, picking up speed before crashing through the nursery fence and hitting a group of small children playing in the garden, some of whom were trapped under the vehicle.

One boy, identified as four-year-old Tommaso D'Agostino, died after the impact, while five others were hospitalised.

Two four-year-old girls were flown by helicopter to the Gemelli hospital in Rome, with one in a serious condition, while another child is being treated at the Bambino Gesù hospital in the capital.

The most likely hypothesis, according to Italian media reports, is that the boy in the car released the handbrake, either by accident or while playing.

The owner of the car, a 38-year-old Bulgarian woman, is being investigated for vehicular homicide.

In addition to those injured, other children were in shock. Parents raced to the school, 45 minutes earlier than usual, after being notified of the accident.

"When we arrived we found people on the street in tears and the crying of the children made our hearts stop. Around us the ambulances and the police cars, the sirens. We immediately ran inside, making our way through the rescuers, a frightening and surreal scene", the father of one of the 40 children who attend the school told ANSA.

Italy's education minister Patrizio Bianchi expressed his deepest condolences to the families and the school community, while the mayor of L'Aquila, Pierluigi Biondi, declared a period of mourning from 19 May until the funeral of the young boy.

Photo ANSA