A system-wide outage forcing Porter Airlines to ground all of its arriving and departing flights Saturday has been resolved, the airline says.

Flights began departing around 6:30 p.m. approximately two and half hours after the airline announced the outage.

"We will be reviewing the circumstances to determine specifically what caused the issue," airline spokesperson Brad Cicero told CBC News.

"All flights were affected at the time," he said. About 400 passengers were forced to alter their travel plans and five flights were cancelled. Travellers can either fly today, tomorrow or receive a full refund, he added.

During the outage, many passengers were anxious for information and scrambling to rebook.

"They kept telling us pretty much every hour that they'd have an update," said Lawrence Siddall, who was heading home to Thunder Bay after being in Toronto for a medical procedure.

Lawrence Siddall said he waited three hours before learning that a system outage meant he wouldn't by flying out from Toronto Saturday. (CBC)

"Then at the end of that hour they said another hour. And another hour. So who knows?"

Siddall said he waited three hours before finally being told there had been a system failure. But he was grateful for the hotel room voucher provided by the airline.

Mikayla Steele was flying to Sault St. Marie, Ont., with her baby in tow when she heard the announcement.

"Travelling with a baby is quite difficult and it's not fair to people who have to pay for their mistake," Steele said, adding that she's angry, but grateful that the airline is working to accommodate passengers.

Steele is also headed to a hotel tonight and has rebooked a flight for tomorrow afternoon.

The airline, which flies to 23 different destinations in Canada and the United States, was unable to say when the problem came to its attention.