US-based Southwest Airlines will postpone delivery of 67 Boeing 737 Max 8 aircraft by nearly six years.

The move will push $1.9bn in planned capital spending of the company beyond 2020.

However, Southwest Airlines plans to expedite six 737-800 orders to next year from 2018 to help cover the previously announced retirement of its oldest 737 aircraft. The airline aims to expand its fleet by 2% a year through 2018.

The retirement of the airline’s remaining 737-300s will be completed by the third quarter of next year, reported The Dallas Morning News.

"The Max is a fabulous airplane and we will fly it in 2017."

Southwest Airlines said that the change had not altered its plans to take the first delivery of the Max 8, which is Boeing’s newest version of the 737, next year.

The airline’s chief financial officer Tammy Romo was quoted by Bloomberg as saying: "It has nothing to do with the Max.

"The Max is a fabulous airplane and we will fly it in 2017.

"It really is shells, or the number of aircraft."

The 67 postponed Max jets were originally scheduled for delivery between 2019 and 2022, and they will now be delivered in 2023 through 2025.

Under its fleet changes plan, Southwest Airlines will also move up 13 options for Max 8 jets to 2019-2020 from 2027.

The airline is also planning to launch a new reservation system, which will be operational by later this year.