Five planes flew over the annual Rose Parade in Pasadena, California, on Friday writing messages in the sky that included "America is great! Trump is disgusting. Anybody but Trump, US," as onlookers craned their necks for a view.

It was not immediately clear who was behind the airborne protest, targeting Republican presidential front-runner Donald Trump, which coincided with the end of the New Year's Day event that draws hundreds of thousands of visitors to Pasadena, north of Los Angeles.

A spokeswoman for the Trump campaign did not immediately respond to an email seeking comment. The billionaire businessman is seeking his party's nomination for the November presidential election.