Disruption to airline passengers is set to continue after the main airport in Brussels announced it will remain closed for a third day.

Thousands of Britons are being forced to cancel or amend their travel plans after two explosions were detonated in the departures hall of Zaventem Airport on Tuesday.

The airport confirmed it will remain closed on Thursday and there is no set date for reopening.

It issued a statement which read: "Because the forensic investigation is still under way we currently have no access to the building. Until we can assess the damage, it remains unclear when we can resume operations."

Around 60 Brussels Airlines flights would normally have operated between the Belgian capital and British airports such as Birmingham, Manchester and Edinburgh during the three-day closure.

British Airways has so far cancelled 29 services that would have flown either into or out of Heathrow.

BMI Regional was also forced to suspend its Brussels flights at East Midlands and Newcastle airports.

Affected Brussels Airlines passengers who booked through the carrier's website are able to request a refund or rebook for a new date of travel before June 30.

BA is allowing passengers whose flights have been cancelled to alter their itinerary or claim a full refund.

Travellers due to fly between Friday and Tuesday are being given the opportunity to rebook to a later date or an alternative destination.

Aviation consultant John Strickland said the disruption is "a headache for any airline" because the closure of a major airport "comes up with no warning and it's not something you can easily plan for".

He said that airlines are being "very pragmatic" by offering refunds and rebooking options, but noted that "there isn't really any other approach they can take".

Some passengers will use neighbouring major airports such as Paris or Amsterdam, but they will have to make their own arrangements for road or rail travel to or from Belgium, Mr Strickland said.

Many BA customers will be due to connect to long-haul flights at Heathrow, resulting in a complicated process of altering itineraries, he added.

"Airlines have to reappraise not every day but every hour or so," Mr Strickland said. "It's a continuous process."

Eurostar trains to Brussels were suspended following Tuesday's attacks, with services from London terminating at the French city of Lille.

Services returned to normal on Wednesday although passengers were advised to allow one hour to check in due to enhanced security checks at stations.

Passengers who no longer wish to travel to the Belgian capital on Wednesday can claim a refund or rebook.

Security has also been stepped up at transport hubs in the UK.

A spokesman for Heathrow said: "In the light of events in Brussels Airport we are working with the police at Heathrow who are providing a high-visibility presence."

Gatwick issued a statement which read: "As a result of the terrible incidents in Brussels we have increased our security presence and patrols around the airport."

The Foreign and Commonwealth Office (FCO) updated its travel advice for Britons in the city, urging them to "remain vigilant and follow the instructions of the Belgian authorities".

Anyone who is concerned about family or friends in Brussels can contact the FCO's helpline on 0207 008 0000.

A spokesman for travel organisation Abta said British holidaymakers due to visit the city should contact their transport provider.

He added that although Belgium is a popular destination for UK visitors, March is "one of the quieter months for leisure travel".