Toronto's Pearson International Airport and the Canada Border Services Agency said Thursday that a new plan would resolve a serious overnight backlog at customs that forced thousands of travellers to wait in line up to three hours.

Officials said that as of Thursday afternoon, crowds were under control following a situation on Wednesday evening in which March Break vacationers arrived home to bedlam at Canada's busiest airport.

Travel-weary flyers arrived at Terminal 1 only to be confronted with hordes of others waiting in line to get into the area where customs officers process travellers.

Vanessa Barrasa, a spokeswoman for the CBSA, said the lineups began in the mid-afternoon Wednesday. Although the agency called in a few more border guards so that 17 booths were staffed, it wasn't enough.

Barrasa said the staffing levels were based on information from the Greater Toronto Airports Authority (GTAA).

Scott Armstrong, a spokesman for the authority, which works with airlines to schedule flights, said the situation on Wednesday night was "entirely unacceptable," but promised it wouldn't happen again.

Both the GTAA and CBSA say they have revised their plan, and have extra staff and management present, as well as rotating teams to cover breaks.

Some travellers on Wednesday had estimated up to 5,000 people were in line, while others said the number was closer to 1,000.

"It just turns you off flying. Doesn't say much for the Toronto airport authority," said John Gorman, who flew in from Los Angeles at around 8:20 p.m. ET and waited at least two hours to clear customs.

"Some people were sick, and kids crying. It was just an unsafe situation."

Higher volumes expected this weekend

About 4,000 people arrived at the airport in about an hour, which isn't out of the ordinary, but it appears there was some disorganization around staffing levels, said Armstrong.

"It's entirely unacceptable for passengers, especially after a long flight, to arrive and then be expected to wait such a long time to get into the customs hall," he said.

"What we're trying to figure out today is: what happened, what information was missing and who was missing it."

Armstrong said the airport is expecting higher volumes this weekend as March Break for thousands of schoolchildren wraps up. The CBSA said the long delays Wednesday were due to "a convergence of flights and higher passenger loads."

Mike Bornhorst, who flew in from Chicago, said it was his "second worst" flying experience, behind having to sit in an aircraft for eight hours on a runway.

"They said they didn't have enough people working there. It seemed ridiculous," he said about Wednesday's incident.

"And there's no bathrooms. So people had to continuously run back to a bathroom that was like a quarter of a mile away."

'This couldn't possibly be the line'

Carl De Leon said the long lineups on Wednesday prompted acts of kindness from some passengers, who tried to get elderly people to the front of the line, including one older couple who had been flying for 24 hours after leaving Australia.

Others tried to make the best of the situation. Amina Moreau got off her plane and was aghast at the mass of people gathered in the area where she disembarked.

"I just thought 'this couldn't possibly be the line to customs,'" she said.

But she said she was through customs in an hour, compared to her original estimate of five hours.

"I'm going home with a smile. I had a good vacation," Moreau said.

"I took some pictures and some video clips, and I actually had the time of my life doing it and got some pretty weird looks from people."

Pearson is Canada's largest and busiest airport, with 30.4 million passengers travelling through in 2009. About 87,000 passengers travel through the airport every day.