Boston was on high alert Tuesday with extra security measures put in place across the city after three explosions took the lives of more than 30 people in Brussels.

The security measures include expanded security by both MBTA Police and Massachusetts State Police in transportation hubs around the city, with additional officers stationed at Logan Airport and T stations

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“Out of an abundance of caution, MBTA personnel and police are stepping up their vigilance and visibility today,” Massachusetts Bay Transportation Authority spokesman Joe Pesaturo said in a statement Tuesday. “The ‘See Something, Say Something’ message is being heard throughout the system to encourage customers to report any unusual activity.”

State and city officials and law enforcement have said there is no reason to believe Boston is at risk, but that security measures would be in place regardless. 

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“As always, a multi-layered security plan is in place at the airports and seaports,” State Police spokesman David Procopio said in a statement. “While we do not discuss specific tactics and deployments, security operations at those facilities is constantly evolving to address current situational awareness.”

"There is no known threat credible or otherwise against the #MBTA, TPD officers will be highly visible & vigilant," the MBTA Transit Police tweeted.

"While there has been no credible threat to MA, security has been strengthened for our public transit systems and airports," tweeted Gov. Charlie Baker, adding that state and federal officials are sharing information.