This is the astonishing moment a book was apparently hurled at the head of President Barack Obama during a campaign rally in Philadelphia.

The flying missile narrowly missed hitting the President yesterday.

It is not clear what the book was, where it came from in the crowd, or why it was thrown at Mr Obama – who did not appear to notice the danger.

Duck, Mr President! A book narrowly misses Barack Obama's head after it is thrown on stage during a rally in Philadelphia todayDuck, Mr President! A book narrowly misses Barack Obama’s head after it is thrown on stage during a rally in Philadelphia today

Close call: It is not clear where the book came from in the crowd - or what type of book it wasClose call: It is not clear where the book came from in the crowd – or what type of book it was

But it is expected that there will be fallout from the security breach as the Secret Service investigates how close the President came to danger.

The rally was clearly an eventful one – other images showed a naked man being led away in handcuffs by police.