TORONTO - Porter Airlines says its operations are returning to normal after a technical problem grounded all its flights Saturday afternoon.

The Toronto-based airline blamed the problem on a system outage, but didn't immediately have a specific cause.

Aircraft were grounded for about two hours and five flights were cancelled.

Porter said in an email that about 400 passengers were affected, they were given a choice of rescheduling their travel plans or get a refund.

Porter operates flights out of Toronto's island airport to and from cities in Central and Eastern Canada, and seven locations in the U.S.