MITT Romney was set to deliver a make-or-break speech to America early today putting himself forward as the man who can revive the world's largest economy even as a new poll showed him to be the least popular presidential candidate in almost 30 years.

Up to 40 million Americans were expected to tune in to the speech at the Republican National Convention in Tampa, Florida, which offers Mr Romney by far his biggest chance yet to persuade voters he can create jobs and boost shrinking wage packets.

Mr Romney was under enormous pressure to deliver an inspirational speech after a lacklustre convention dogged by a hurricane, poor poll figures and doubts among delegates about his ability as a campaigner.

His speech at the party convention in Tampa formally accepting the party's presidential nomination is one of his last major opportunities to fire up party supporters and win over floating voters before the White House election in November.