A runner falls in front of a Cebada Gago ranch bull along Estafeta street during the second running of the bulls at the San Fermin festival in Pamplona.

Pamplona - Charging bulls injured 14 people during the annual San Fermin festival in the northern Spanish city of Pamplona, local officials said.

Those hurt as bulls were let loose through the city's narrow streets included four US citizens, an Indian, a Portuguese a Briton and a South African, according to the local government.

A South African man, 73, and a 58-year-old Spanish resident of Pamplona were in a serious condition after being gored, the Navarre regional government said on its website.

Two other Americans and an Indian were also gored without sustaining serious injuries, it said.

A 53-year-old American woman was hospitalised for trauma.

Pamplona is host to the most famous of Spain's many bull-running festivals, where hundreds of people try to outrun six charging bulls over 800 metres.

As often happens, on Friday bulls tossed several people into the air and pinned others to the ground as participants pulled their tails and grabbed their horns.

Ahead of this year's festival, organisers warned participants they could die in the bull run, pointing out that at least 16 people had been killed since 1910.

The most recent fatality was in 2009.

On Thursday, five people were injured.

After being let loose through the streets, the animals are killed during bullfights later in the day.