All public transport was shut down in the Belgian capital following blasts at the city's Zaventem airport and at a Metro station earlier today.
The airport will remain closed tomorrow, with airport authorities having previously said "it is impossible for us to say when operations will be resumed".
Public transport has started operating in the Belgian capital again this evening. Most metro services are not running tonight, but some lines have partially reopened.
The attacks prompted a growing number of European nations to announce reviews of their security procedures.
We've enabled free changes / refunds to guests travelling to #Brussels on EI631/638/639 today 22Mar16 and EI630/631/638/639 tomorrow 23Mar16
— Aer Lingus (@AerLingus) March 22, 2016
Aer Lingus will offer affected passengers refunds or free flight changes for passengers affected by the on-going situation in the Belgian capital.
Following an incident at #Brussels #Zavantem, EI630 has diverted to AMS, and airport operations at @BrusselsAirport have been suspended.
— Aer Lingus (@AerLingus) March 22, 2016
The airline was also forced to divert the Brussels-bound flight EI630 to Amsterdam.
All Aer Lingus flights to Brussels tomorrow have also been cancelled due to the continued closure of Brussels Zaventem.
Meanwhile, Ryanair says flights that were due to operate to and from Brussels Zaventem tomorrow will now operate to and from Brussels Charleroi.
"Customers booked to fly from Brussels should make their way to Brussels Charleroi and allow extra time for their journey," the airline says.
Ryanair will also offer refunds and free transfers: "Customers whose flights have been cancelled can apply for a full refund or transfer to the next available flight. Customers booked to travel to/from Brussels Zaventem today or tomorrow, can transfer onto another flight free of charge within the next 2 weeks," the company told Newstalk.
An additional post on Ryanair's website read, "Our flights to Alicante, Barcelona and Dublin have been cancelled and a number of flights have diverted to Brussels Charleroi. Customers travelling to/from Brussels Zaventem today should check the Ryanair.com website before travelling to the airport."
Passengers intending to travel to Brussels today should contact their airline for latest flight info before coming to @DublinAirport today.
— Dublin Airport (@DublinAirport) March 22, 2016
Dublin Airport has also advised passengers with flights booked to Brussels to contact the airlines that they have booked with before travelling to the airport.
Heathrow and Gatwick airports were among those confirming such moves in the UK while the Dutch government said it was also examining its Belgian border controls, with extra police deployed.
An increased level of visible security has also been seen in London's Heathrow Airport.
Travellers reported delays and a heavy police presence at Amsterdam's Schiphol Airport. The Dutch railways operator said trains heading south to Belgium were subject to indefinite delays.
