Brussels Airlines is restarting some commercial flights from Belgium on Thursday, using Liege and Antwerp airports, while Brussels Airport remains closed until further notice due to the attacks at on March 22nd.

Security was tightened across Europe, just four months after coordinated attacks in Paris killed 130 people.

Belgian police were hunting on Thursday for a "third man" filmed with two Islamic State suicide bombers at Brussels Zaventem Airport as evidence accumulated that the same jihadist network was involved in the deadly Paris attacks last November.

But apprehension about travel, at least Tuesday, was global.

American Airlines (AAL - Get Report) stock is down by 2.51% to $42.38 in mid-morning trading on Tuesday, after terrorist attacks in Brussels this morning, which has caused stocks to retreat.

Out of the top European airlines companies, Norwegian airlines, Turkish Airlines and Air France-KLM took the biggest hits on Wall Street, which were trading down 5.90 percent, 4.77 percent and 3.96 percent, respectively, according to Google Finance.

Delta Air Lines Inc. and United Continental Holdings Inc. are all down.

- Hyatt Hotels Corp. fell 1.8 percent to $48.93.

Reports of man with gun at Naval Medical Center in San Diego
No injuries were reported, and investigators found no evidence of a shooting after the facility was shut down for several hours. Navy's Pacific Fleet. "Four unspent bullets were discovered during security sweeps of the Naval Medical Center".

- Intercontinental Hotels Group PLC fell 2.7 percent to $39.63.

Among Dow blue chips, Pfizer led with a 1.0 percent rise while Goldman Sachs topped losers down 2.1 percent.

- Starwood Hotels & Resorts Worldwide Inc. fell 1.6 percent to $82.88.

- The Priceline Group Inc. down 2.3 percent to $1,319.41.

- TripAdvisor Inc. down 2.5 percent to $64.04.

- Thomas Cook PLC down 6 percent to 87 pence, or $1.24.

The France-U.K. train tunnel operator Groupe Eurotunnel SE was down 3.8 percent to 9.63 euros, or $10.80.