A few hours after nine Catalan separatist leaders were sentenced to between nine and 13 years in prison for their role in a failed independence bid, protesters shut down Barcelona airport.

It is certainly not the first time that thousands of independence supporters have taken to the streets for the cause but the airport has never before been the epicentre of the action.

Some saw the images that came out of Barcelona's El Prat Airport as a clear sign of the influence of demonstrations in Hong Kong.

After the leaders' sentences were revealed, pro-independence group Tsunami Democratic called for demonstrators to "immediately and by all possible means" bring Barcelona airport to a halt.

The avalanche of protesters that descended on the building caused chaos with hundreds of flights cancelled — Spanish low-cost airline the airline Vueling said it had to cancel 120 flights.

Steve Tsang, director of the China Institute at the SOAS University of London, told Euronews he understands why Catalan protesters used the same method as those in Hong Kong.

"If you move the protests to an international, main airport, which is essentially what the protesters in Hong Kong did, you can get international attention immediately because you are affecting people who are travelling," he said.

"If your goal is to get international attention, this is an effective way to do it."

"Tsunami Democratic comes from the Catalan tradition of nonviolent resistance but, obviously, we have learned from other similar movements," the organizers of the protests at the airport told Euronews.

"More than just inspiration, there is reciprocal and constant learning."

But can the reason for the protests really be compared? Tsang believes that any parallels are more technical than political.

In both cases, there are claims of autonomy and independence but protesters in Hong Kong are not calling for the same thing as those in Catalonia, he said.

"They (Hong Kong protesters) are not asking for self-determination — they have simply asked the Chinese Government to maintain an agreement so that Hong Kong maintains a high degree of autonomy," Tsang added.

Demonstrators in Catalonia want self-determination, which could potentially lead to independence.

He also added that protesters in Hong Kong are dealing with "a very hard authoritarian regime, without any democratic responsibility," but that in Catalonia, even though demonstrators "see many problems with the government, the government of Spain is democratically elected."

In Barcelona, emergency services were called out to treat 13 people throughout the day, although none had serious injuries.

According to Tsang, protesters in Hong Kong, like those in Catalonia, have argued they acted peacefully and that if they became violent it was because of police presence and reactions.

How were protests organised in Catalonia?

"We will find out who is behind the Democratic Tsunami," Spanish Interior Minister Fernando Grande-Marlaska said, adding his department was already investigating the movement.

The group, which uses social networks to get instructions to its followers, emerged on September 2.

It used Twitter to call on its supporters to use "civil disobedience" and "non-violent actions" in response to the upcoming court ruling.

Democratic Tsunami does not have visible spokespeople or leaders, a feature it shares with the Committees for the Defense of the Republic (CDR) — a web of committees whose initial function was to facilitate the Catalan independence referendum.

However, unlike the CDR, the movement does not function via decentralised groups, but rather as a network that works to develop strategies.