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In the wake of Wednesday's deadly attacks just out side of London’s Parliament, many visitors are wondering how safe the city is now as they scramble for information.

Police in London are treating the attack as an act of terrorism, one of the most serious since the bus and train bombings that took place more than a decade ago.

Thursday, many tourists within the country expressed concern online, while those with travel plans to the U.K. are wondering whether to cancel.

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“I was planning to go to #London for tourism but that city is no longer safe. I canceled my plan, I'm extremely worried,” one potential traveler to London posted on Twitter.

Brianna Glenn, owner of Milk & Honey Travel, told Fox News that over the last couple of years, she’s seen quite a few of these types of events that often occur in areas frequented by tourists.

“I have people going to London next month, and they’ll come to me and ask me about cancelling, and what are the risks. I’ll discuss it with them,” Glenn said.

“But we have to be realistic and understanding that safety can’t be accurately predicted. We have to be sensible about risks, but I don’t want them to cheat themselves and live inside a safety bubble."

One of the biggest terrorist attacks in London occurred July 7, 2005. Sometimes referred to as "7/7," the series of synchronized terrorist suicide bombings in the central city targeted civilians using the public transport system during rush hour.

But Wednesday's attacks are unlikely to have any lasting effect, say tourism industry insider.

David Scowsill, the president and CEO of the World Travel & Tourism Council (WTTC) told Fox News via email that his organization is "deeply saddened by yesterday's attack" but knows the city will remain strong.

He continued, "England and London specifically are very resilient tourism destinations. We do not expect this isolated incident to have an impact on people's decision to travel to the country nor its capital.

"As the security forces are investigating the attack, Londoners continue with their daily lives."

But more recently, France-- another major destination for American tourists-- has been hit hard by a series of devastating attacks. After the 2016 attacks in Nice, France, Glenn said she had one cancellation-- but that client wasn't even traveling to France.

"Sometimes it’s irrational," Glenn admitted but still, she recommends that all travelers purchase travel insurance for big trips. "I’ve had people change routes of flights to avoid certain airports."

Wednesday’s tragic event took place in one of London’s most populated areas, near Parliament Square.

Steve Born, vice president of marketing for the Globus Family of Brands, told Fox News that across his company they currently have 69 guests in London, and all are accounted for in their home base hotels. A few guests are staying near the location of the attack.

“Nine of the 69 tourists were staying at the Park Plaza Westminster hotel, so there was a logistical situation for them given traffic and getting them to maneuver around Parliament House,” Born said.

“They had a theater night pre-scheduled, and we gave them the option to change plans or continue on. They all chose to continue, which speaks to the level of comfort in London, and now that they know everything is under control, they can continue to enjoy their vacation,” he added.

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Nearly ten percent of tourists in Britain last year came from the U.S., according to government statistics. In 2015, France, the U.S., and Germany were the top three markets to visit the U.K. accounting for 30 percent of the country's visitors, according to Visit Britian. In the first nine months of 2016, the English capital welcomed a record 14 million foreign visitors. 

Several tourist attractions were immediately impacted by Wednesday’s attack.

Not far from Parliament, The London Eye, one of the city’s most popular attractions, was shut down as the attack unfolded, trapping hundreds of guests inside until police secured the area.

The London Eye tweeted, “We will always take every precaution to ensure the safety and security of our guests and staff.”

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The attraction reopened Thursday afternoon, local time.

Members of Parliament were evacuated to Westminster Abbey until police had the attack under control.

The Abbey followed by closing to visitors for the day. Today, it is only open to those attending worship services.

According to Metro UK, police are advising tourists to avoid traveling to or through several highly trafficked areas Thursday including the following places:

--Parliament Square

--Westminster Bridge (closed to traffic both ways for the ongoing investigation)

--Lambeth Bridge

Tube passengers may travel through the Westminster station but will not be allowed outside the station. And those with planned river tours down the Thames should note that boats not allowed to sail west of Blackfriars near Westminster. Police are also urging visitors to report any suspicious activity to authorities immediately.