Police in British Columbia are searching for a person who made a threatening phone call that forced the shutdown of 21 sailings and stranded thousands of summer travellers for several hours on Saturday.

B.C. Ferries is putting new security measures in place after a bomb threat was called in to 911 from a mall in Coquitlam.

On Sunday, passengers boarded vessels without having their vehicles checked or their luggage screened. But B.C Ferries spokesperson Deborah Marshall said terminals will have increased security, even though passengers wouldn't be able to notice a difference.

She said she couldn't disclose what new measures are taking place but that they are being extra vigilant after Saturday's scare.

David Hahn, chief operating officer of B.C. Ferries, said the threat came in a 911 call to police around 3:30 p.m. on Saturday from a Coquitlam mall.

However, it was the third such threat in recent months.

"I think it's atrocious," he told CTV News. "I'd like to see it really dealt with. I'd like to see them catch this person and hold him accountable."

B.C. Ferries is offering a $50,000 reward for information on the caller who is described as a man with a Middle Eastern accent.

"Whether it was a Middle Eastern caller is a different issue, but that was the accent they were using," Hahn told the Canadian Press earlier Sunday.

Terrorism experts say it is unlikely the call was made by a credible threat.

"The jihadist movement doesn't threaten, they just attack," terrorism expert John Thompson said in a sit-down with CTV Newsnet.

Thompson said despite the probability that the bomb threat was a hoax, there is no room for error.

"You have to treat every threat as credible and investigate it," Thompson said. "With public transit, because it has to be so accessible, the threat is much more profound."

Ticket sales were stopped and passengers were evacuated from a number of vessels that had already left port when the call came in.

Travellers who had yet to depart were held in terminals in Vancouver, Victoria and Nanaimo until their vehicles were searched by police and bomb-sniffing dogs.

All vehicles in the crowded parking lot of Tsawwassen terminal, which is a 40-minute drive south of Vancouver, were also searched.

"Those people were there for a God-awful long time," Hahn said.

"This was a very specific type of bomb threat that was reported . . . The RCMP had every vehicle, every bus, every camper, checked."

Ships sail between Tsawwassen and Swartz Bay almost hourly. Larger vessels carry up to 470 vehicles and 2,100 passengers. Everything was back to normal by Sunday.

Even with bomb threats occurring regularly, Hahn said the extent of the precautions taken by authorities on Saturday showed there was some weight to the threat.

"I would say that this is one that, for whatever reason, the RCMP gave more credibility," he said.

Nonetheless, police spokeswoman Sharlene Brooks said finding the culprit might not be so easy.

"Unless someone comes forward that has personal knowledge of the individual that may have made this call, identifying this suspect may be next to impossible," she said.

In May, Transport Canada gave the Ferry corporation $3.9 million to increase security. The money will be going towards installing more lighting and fencing plus closed-circuit cameras.

With a report from CTV British Columbia's Dave Lefebvre and files from The Canadian Press