Gardaí say that shortly before 5pm, they and other emergency services were alerted after a number of onlookers were injured “in an incident involving a participating car” at Trentagh, near Kilmacrennan.

Tadhg was taken by ambulance from the scene to Letterkenny University Hospital, where he was later pronounced dead.

Two other spectators are receiving hospital treatment for non-life-threatening injuries.

Gardaí said the local coroner has been notified, a post-mortem examination will be arranged and that the scene has been preserved for a technical examination.

It is understood the crash happened when a competing car left the road at a left-hand bend.

In a statement on Saturday, Motorsport Ireland and Donegal Motor Club said they cancelled the remainder of the event “as a mark of respect”.

They said they were “deeply saddened” by what had happened and expressed “deepest sympathies to the family of the deceased and ask that everyone respect their privacy at this time”.

Motorsport Ireland said that as the country’s governing body for four-wheeled motorsport, it, along with Gardaí, has begun “a full investigation into the circumstances of the accident”.

Both the organisation and the Gardaí say they are aware video footage of the accident is circulating on social media and have asked the public not to share it.

The three-day event bills itself as “one of the toughest rally challenges there is for drivers and teams”.

Participants compete in 20 stages around the north-west coast of the county.

Organisers say it attracts more than 70,000 spectators and almost 400,000 view the rally on TV and online.