Three people were gored and a further two people suffered head trauma during the first day of Spain's best-known bull-running festival in the northern town of Pamplona this morning, the Red Cross has said.

One man was loaded into an ambulance on a stretcher shortly after the dash through the medieval town centre's narrow streets to the bullring, which lasted two minutes and 41 seconds.

A total of 53 people were treated by the Red Cross.

Authorities said in a statement that those hurt included two US citizens, aged 23 and 46, and a Spaniard, who was injured in his left thigh.

Local media reported one of those gored was in a serious condition.

Thousands of runners, dressed head to toe in white, with bright-red neckerchiefs, gather every year for the traditional morning run, after which the animals are kept in the bullring until the afternoon's fights.

Anyone over the age of 18 can participate in the Pamplona runs though authorities warn of the risks.

Since 1911, 16 people have been killed in the event, the last one in 2009.

This year, the bulls were from cattle breeder Puerto de San Lorenzo, whose bulls have been responsible for one goring in the past.

One person was gored on the opening day of the festival last year.

Locals and tourists alike will join in the 8am run every morning until next Sunday.

The festival regularly stokes debate about the treatment of animals.

On Friday, protesters laid half-naked on the street with fake spears coming out of their backs to protest against what they see as cruelty.