TORONTO -- A pair of Canadian student travellers bemoaning what appeared to be a routine delay aboard their train through Italy instead learned they were just minutes from a disastrous bridge collapse that killed at least 20 people on Tuesday.

Speaking from the train shortly after the tragedy, Tamar Bresge, 23, said she and her friend Melissa Light, 22, both of Toronto, were still processing what had happened.

"Our train would have gone under it in minutes, like less than five minutes," Bresge said. "We just missed it, like just missed it."

A huge section of the Morandi Bridge -- on a main highway linking Italy and France -- collapsed Tuesday in the port city of Genoa during a sudden violent storm, sending vehicles and tonnes of twisted steel and concrete plunging 45 metres into a heap of rubble below. Italian officials said at least 20 people were killed and others injured.

Bresge and Light were en route from Nice in France to Milan when the sunshine they were in gave way to a fierce storm.

"There was really bad thunder and lightning when it collapsed, so I thought I was just hearing thunder but we were so close that I probably heard something collapsing and just thought it was part of the storm," Bresge said.

The train made an unscheduled stop at the airport station in Genoa after earlier short delays. Without giving details, train staff announced the delay was indefinite and for the first while, the pair didn't know what was happening. People thought it was a typical train delay.

"Everyone collectively groaned," Bresge said.

It was only after the train stopped that the two Canadian women, who do not speak Italian, began to learn of what had happened from fellow passengers.

One passenger near them sounded agitated, while others began explaining the disaster, or showed pictures from the scene on phones, the pair said. The enormity of what was unfolding a few hundred metres further began dawning.

"We thought at first that it was a train crash. Then we understood a bridge collapsed," Bresge said. "We were stopped so close to the site, we could hear sirens going."

When her father in Toronto awoke, he called her and played news of the incident over the phone, allowing them to finally understand exactly what they had just missed, she said.

After about two hours, the train moved on into Genoa, allowing them to see the bridge in the distance.

"It was completely severed. There was a completely empty portion," Light said. "It's crazy. We both feel very grateful that we were on the train before the crash and not underneath it. It definitely feels surreal."

The collapse occurred on the eve of a major Italian summer holiday -- the high point of the season when most cities and business are closed and people head to the beaches or the mountains. The 50-year-old Morandi Bridge connects the A10 highway to France and the A7 highway that continues north toward Milan. It is 45 metres high and just over one kilometre long.

The Canadian women said they planned to check into their hotel in Milan, rest up and then try to process what happened.

"We weren't so annoyed about the delays," Light said. "We were just grateful that it wasn't us."