As the Bay Area continues to react to Tuesday's terror attacks in Brussels, experts say that cities like San Francisco should brace for similar attacks and change security measures in vulnerable areas like those targeted this week.

Last night, both San Francisco City Hall and San Francisco International Airport were bathed in the colors of the Belgian flag in solidarity with Brussels, which was struck by three bombings yesterday that killed at least 30 people and injured at least 230.

Two of the explosions were in the Brussels airport, the third on a train as it left a subway station. Though local officials say that there is "no credible threat" posed in the Bay Area, SFPD, BART police, and security at SFO were all on high alert following the attacks. But is that enough? Former FBI Agent Rick Smith tells KRON 4 that it's likely not, saying that “It’s coming here, folks. It’s coming to this country soon...Be aware of it. Be awake. Be vigilant.”

A TSA agent at SFO expressed similar concerns to the Chron, saying that "Any dingbat can just take something and hide it under their shirt or in their bag and walk in here and blow up the place."

That agent called for "screening of passengers before they enter the terminals," a stance with which SoCal Congresswoman Janice Hahn, among others, agrees, the Wall Street Journal reports, saying that Hahn "called on the U.S. Transportation Security Administration to expand security perimeters at American airports in response to the attacks."

However, it might not be that easy, the WSJ says, as "pushing checks out further could raise other security issues, industry executives say, and add costs and delays that may outweigh any security benefit." According to one aviation security expert, no matter where to put the security perimeter “you still have the queues. If you cause congestion, a whole lot of people crammed together, it’s a target-rich environment no matter where it is. A big crowd is a target.”

Back in San Francisco, however, Belgians and their friends were more focused on the present than the future. At a vigil at SF's City Hall Tuesday night, about 100 people sang the Belgium national anthem and held a moment of silence for the victims, KRON 4 reports.

"My heart is with all the people in Belgium, my family and friends, but also my Belgium friends here in the Bay Area. I have not heard from everybody, and I'm sure they may have some people affected," Leslie DeSaeyere, a native of Belgium, told ABC 7 from the vigil.

"Many held up three fingers, a symbol affirming their respect and allegiance in their home country," KTVU reports. "I'm in shock. Now I'm just numb. I've gone through all those stages: anger, sadness confusion," Virgine De Paepe said from the vigil.

"It's just hard to know that the only thing we can do to show our support is to gather here, but I think it does make a difference because it shows the world is watching," said Alex de Hemptinne, a UC Berkeley student from Belgium.

According to ABC 7, Bay Area Muslims were quick to condemn the terror attacks, for which the Islamic State has claimed responsibility.

"They have their own desires, political or whatever, but Islam has nothing to do with this, and we need people to step up to the plate and counter this ideology," Zaki Agha of Bay Point's Ahmadiyya Muslim Community said.

According to the Belgian Trade Commission, there are about 5,000 Belgians in the Bay Area. Nathalie Delrue-Mcguire, who was appointed by the King of Belgium as the Honorary Consul of Belgium in San Francisco on July 1st, 2013, urges all of them to band together in this time of strife.

"The best message is to stand in solidity - show our support, show our love," she says.

"That’s very important and also not be scared."

Les trois couleurs du drapeau belgique

A photo posted by Sol Fung (@solfung) on

Previously: In Wake Of Brussels Bombings, SF And BART Police On Heightened Alert