Michelle Obama has taken aim at Republican White House hopeful Donald Trump, saying "a president can’t just pop off" when he or she is upset.

Speaking at a rally in Philadelphia for Democratic nominee Hillary Clinton, the first lady said: "We need someone who is steady and measured, because when making life-or-death, war-or-peace decisions, a president can’t just pop off or lash out irrationally. No, we need an adult in the White House."

While Mrs Obama did not mention the businessman by name, she left little doubt whom she was referring to as she condemned the birther movement's "hurtful, deceitful questions" aimed at undermining her husband's presidency.