Eighteen people on a stag do have been injured, including three seriously, after a trailer carrying the partygoers overturned on a steep hill in Switzerland.

Seventeen of the revellers were being pulled by a tractor driven by another person when the incident happened on Saturday evening (22 July).

At around 7pm, as the vehicle travelled down a steep hill, the weight of the trailer and its passengers began pushing the tractor forward.

The driver pressed on the brakes in a desperate attempt to slow the vehicle down but lost control, police said.

Both the trailer and the tractor then flipped over, injuring all 18 people.

The incident, along Hochwachtstrasse in the town of Wohlen, 10 miles west of Zurich, left three of the party with serious head, back and pelvic injuries.

One woman who lives on the road where the accident happened told local media: "It was terrible. Everywhere there were people on the ground who had been thrown out of the tractor trailer during the accident."

Two rescue helicopters, police and fire fighters attended the scene. All the injured were transferred to eight hospitals in the region.

Emergency workers spent hours trying to clear the trailer, tractor and debris from the road.

Police are now investigating whether the driver of the tractor should be charged for negligence or road traffic violations.

A wife of one of the those seriously injured told local news site Blick.Ch: "My husband suffered severe hemorrhages and was flown to Zurich. He was put in an artificial coma."

After hours of anxiety she was able to speak to him for a short while. She said she does not blame the driver of the tractor for the accident.

"He blames himself, but I do not blame him for the accident. It was the responsibility of each guest whether they wanted to get into the trailer or not. No one was forced," she said.