The New Jersey governor tells NBC's "Today" show Romney should "put them out sooner than later because it's always better to have full disclosure."
Romney's taxes have emerged as an issue days before the South Carolina primary. He agreed in Monday night's debate to consider making his tax returns public, and then committed to releasing them on Tuesday.
But the multi-millionaire candidate now is on the defensive after acknowledging that his effective tax rate is 15 percent, saying most of his income came from investments and speeches rather than earned income. Christie says he wants to remain as governor, but he wouldn't rule out joining a Romney ticket.