British actor Daniel Radcliffe missed his first day at California's Comic-Con convention on Thursday (24Jul14) after he was reportedly stranded in Canada due to visa problems.

The Harry Potter star had been in Toronto to premiere his new movie What If ahead of a planned trip to Comic-Con, but he was unable to leave the country due to an issue with his work visa which left him unable to enter the U.S.

A source tells New York Post gossip column Page Six, "He's stuck in Toronto with visa problems."

Editors of the publication report Radcliffe is currently in the process of upgrading his work visa to a permit which will grant him a three-year stay in America, and needed a stamp from the U.S. embassy in Toronto to approve the paperwork.

However, Radcliffe was reportedly unable to obtain the stamp in time because the embassy's computer network was suffering technical problems.

The actor is expected to attend Comic-Con on Friday (25Jul14) to promote his film Horns, but it is not yet known whether his travel dilemma has been resolved.