UFO spotters have been left wondering who or what was following Republican hopeful Donald Trump's helicopter as it flew over a fair during his campaign.

The snapper, who has not been named, captured this "blob" following closely behind the Trump Towers tycoon's chopper as it flew a group of children over the Iowa state fair.

The witness, who has reported it to a US national UFO database, said: "Donald Trump was at the Iowa State Fair giving kids a ride in his helicopter.