Police in New York are investigating an envelope containing a white powdery substance that was sent to Hillary Clinton's campaign, forcing an office to be evacuated.

A spokesman for the New York Police Department said the envelope was found at Mrs Clinton's Manhattan office, where mail is received, on Friday evening. It was then taken to the 11th floor of her Brooklyn headquarters.

The discovery of the suspicious substance caused that floor to be evacuated. There were no reports of illness or injury.

It was not immediately known what the substance is or whether it is harmful.