Miami: A Miami defence lawyer's pants burst into flames in court just as he began his closing arguments in front of a jury - in an arson case.

Stephen Gutierrez, who was arguing that his client's car spontaneously combusted and was not intentionally set on fire, had been fiddling in his pocket as he was about to address jurors on Wednesday when smoke began billowing out his right pocket, witnesses told the Miami Herald.

Stephen Gutierrez in a photo from his firm's website.

He rushed out of the Miami courtroom, leaving spectators stunned. After jurors were ushered out, Gutierrez returned unharmed, with a singed pocket, and insisted it wasn't a staged defence demonstration gone wrong, observers said.

Instead, Gutierrez blamed a faulty battery in an e-cigarette, witnesses said.