Expansion of Heathrow airport has been approved by a committee of ministers, according to BBC.
Ministers approved the decision at the cabinet committee meeting on Tuesday morning.
However, Downing Street has yet to officially confirm the decision.
Transport Secretary Chris Grayling will make a statement to the House of Commons around lunchtime on Tuesday, But the decision faces a long consultation before it becomes final.
A study last year, led by Sir Howard Davies, recommended a third runway at Heathrow but other options included a new runway at Gatwick or extending one of Heathrow's existing runways.