Russell Crowe had a bit of fun on Twitter yesterday after releasing footage that he claimed was a UFO, four years after it was taken by a cinematographer friend.

The images, purportedly taken over Sydney's Botanic Gardens, have been picked up by hundreds of news outlets all over the world.

The actor released the footage ahead of the release of his film Broken City today. But no one can explain why - although his publicity representative Grant Vandenberg admits Crowe is getting plenty of attention as a result.

"Yes, he tweeted it yesterday - and he has got a movie being released today," he said.