U.S. travel officials, airlines and law enforcement officials are on alert after a deadly bombing at the check-in zone of Brussels airport and the Belgian capital's subway killed at least 26 people on Tuesday.
The Transportation Security Administration is checking on the safety of federal air marshals who were on duty at the Brussels airports this morning or on inbound or outbound flights—a process that officials say will take a while, one official says, because it takes a while to reach people who were off duty. U.S. officials say the TSA Administrator, Peter Neffenger, is in Brussels today on a scheduled trip for meetings with European counterparts.
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The border between France and Belgium was closed and all Eurostar train service to Brussels was halted.
However as long as passengers weren't trying to get to Brussels, the actual ripple effect on travel appeared to be minimal with few slowdowns for American skies. There were only 23 delays and two cancellations at the New York Metro area's airports. Zurich International Airport reported 29 minute delays, according to Flightaware.com.
Delays and cancellations for European travelers were more due to strikes this week by French aviation unions.
Travelers at the Miami airport can expect to see increased K9 patrols, increased uniformed officers, more perimeter patrols and random inspections.
Delta Air Lines and United Airlines rerouted a number of flights following the deadly blasts.
Delta said its flight DL42 from New York to Brussels was diverted to Amsterdam. Another flight, DL80 from Atlanta, had landed safely at the airport and was parked remotely while the airline's local staff worked to safely deplane passengers.
United Airlines, which had two flights due in Brussels on Tuesday morning, said one from Washington Dulles arrived at 7:01 a.m. local time and customers deplaned normally.
The other —Flight 999 from Newark Liberty — was rerouted to another location that the airline did not identify.
United said all remaining flights to and from Brussels International had been suspended until further notice.
Ryanair said its flights to and from Brussels' Charleroi Airport were running, although with some delays.
Starwood Hotels & Resorts Inc. said all Starwood hotels in Brussels were safe but on lockdown, along with the rest of the city.
Facebook Inc. said it activated its "safety check" feature for users after the blasts.
Officials with the Washington D.C. Metro, the region's subway system, said they are taking are also increasing security measures including additional uniformed patrols at major stations and deploying all available transit K-9 teams. Passengers have been asked to remain alert and report anything suspicious.
In New York, officials are the New York City Police Department is closely monitoring the situation in Belgium and is in close contact with international officials and the FBI. NYPD has deployed additional counterterrorism resources to crowded areas and transit locations around the city.
Chicago officials say that while there is no reported threat they do have security protocols in place.
—Reuters and NBC News contributed reporting to this article.
This article first appeared on NBCNews.com.