Nigeria coach Stephen Keshi said Friday he was unperturbed by the attempts of several high-spirited fans to invade the pitch during a training session ahead of their World Cup opener.

Hundreds of football supporters were in the stands of the stadium in Campinas to witness the African champions go through their paces, chanting and waving flags.

But midway through the training session a number of people, mainly young boys, got onto the pitch and attempted to evade security staff as they made a beeline for the players.

One youngster in a Brazil shirt was tackled to the ground before being led away, while a man got as far as a knot of Nigerian players.

But despite the febrile atmosphere in the old concrete stadium in the city near Sao Paulo, the players did not look remotely concerned, focusing on their drills.

Keshi played down the incidents, saying he was not worried.

"These are kids. It's all about emotion and passion," he said. "The kids see the players on TV and now they see them live and they just want to touch their skin, touch them."

At the end of the session the Nigerians waved to the cheering fans in the stands.

Nigeria's first match of the World Cup is on Monday, when they take on Iran in Curitiba in a Group F clash.