Romney votes ahead of last-minute Election Day visits to Ohio, Pa.

GOP presidential candidate Mitt Romney cast his vote in Belmont, Mass., on Tuesday morning.

Romney was accompanied by his wife, Ann, at the Beech Street polling center.

Asked by a reporter whom he voted for, the former Massachusetts governor joked, "I think you know."

The vote is only the start of a busy day for the GOP nominee. With polls showing a tight race nationally and in several key swing states, Romney's campaign announced Monday that the candidate and running mate Rep. Paul Ryan (R-Wis.) would make stops in Ohio, Pennsylvania and Virginia on Election Day.

Romney will travel to Cleveland and then Pittsburgh before hosting his election-night reception at the Boston Convention Center.

Ryan is expected to vote near his home in Janesville, Wis., and then appear in Cleveland and Richmond.

Vice President Biden and his wife, Dr. Jill Biden, cast their votes in Delaware earlier Tuesday. President Obama voted last week in Illinois.

This story was updated at 9:36 a.m.