Ferrovial, meanwhile, already owns 50% of Bristol airport and has complete ownership of Belfast City airport.
Flights from Bristol Airport continue to face delays after snow earlier closed the runway.
Bristol Airport remained open throughout Monday but passengers were warned there may still be disruption to flights.
Flights at Bristol Airport are suspended until 1230 GMT, with no arrivals or departures at Luton before 1200 GMT.
Bristol Airport said all flights were operating as normal with the exception of the Paris Charles de Gaulle route.
After hearing of the sale, Bristol Airport chief executive Robert Sinclair was sceptical that government involvement would be "arm's length".
BBC: Cardiff Airport is sold to the Welsh government for ?52m
The future of Bristol Airport could be threatened by a buyout of Cardiff Airport, a South West MEP has warned.
But despite the stronger position of Bristol Airport, the city's first directly-elected mayor is concerned the takeover will create unfair competition.
BBC: Bristol Airport flies more Welsh passengers than Cardiff
Over the same period, passenger numbers at Bristol Airport rose 1% to more than 5.7m, with 700, 000 of those coming from Wales.
Meanwhile, nearby competitor Bristol Airport, which has sought assurances that Cardiff will not get state handouts, had seen almost six million passengers last year.
BBC: Cardiff Airport is sold to the Welsh government for ?52m
But a spokesman for Bristol Airport said it should already be seen as a second airport for people going in and out of Wales.
He said the purchase "could also provide Cardiff Airport with an unfair advantage over other regional operatives who are not in receipt of government funds, such as Bristol Airport".
The Welsh government is currently negotiating to buy Wales' only international airport from its owners, in a move that one South West England MEP has claimed could threaten Bristol Airport.
Cardiff council's cabinet member for sport, leisure and culture, Huw Thomas, said that as well as being served by Bristol Airport, Cardiff was also only two hours by train from London.
So I think that's the fear of Bristol Airport.
BBC: Bristol Airport flies more Welsh passengers than Cardiff
That's all well and good says Robert Sinclair, who as Chief Executive Officer of Bristol Airport has been watching events in Wales closely and landing a few choice comments along the way.
Robert Sinclair, chief executive officer at Bristol Airport, said they welcomed the mayor's support for fair competition on a level playing field and his comments on the dangers of "special deals on taxation".
BBC: Bristol Airport flies more Welsh passengers than Cardiff
The journey time from Swansea bus station to Bristol Airport has been put at two hours and 45 minutes, while the stage from Cardiff to Bristol will take an hour and 40 minutes.
"It should be noted that not only do the MoD have no objections to this application, neither do the Civil Aviation Authority, nor National Air Traffic Services, nor Bristol Airport, " the firm said.
"To date, 95% of passengers from Bristol International Airport have departed with minimal delays this morning and only five flights have been cancelled from the Airport, " said Andrew Skipp, Bristol International's managing director.
BBC: NEWS | UK | England | Bristol/Somerset | Security stepped up at airports
Rival airport Bristol has raised concerns that Cardiff would unfairly benefit from state support.
The International Airport said a flight to Bristol had been cancelled and all other departures to the rest of the UK were running with slight delays.
He said Cardiff could not compete on a like-for-like basis with Bristol, which was a much bigger airport with two low-cost airlines based there, but needed to focus on "niche opportunities" that it could make work.
Bristol Aero Club was founded for workers at Filton Airport but it was forced to leave the site after its sale to property developers in December.
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