Both brands will continue to exist under the terms of the agreement, which could take up to 18 months to finalise, according to a joint press release.

The combined airlines would have a fleet of 365 narrow and widebody aircraft, and reach 138 destinations.

Based in Seattle, Alaska Airlines mainly serves the western US. The Hawaiian capital of Honolulu would become its second main hub.

Residents of Hawaii would benefit from expanded service to the continental US, the two companies said, and the merger would create “new connections to Asia and throughout the Pacific for travelers across the US”,

The two airlines both provide service to areas “uniquely reliant upon air travel” — the Pacific archipelago and the frontier state of Alaska.

“Commitment to Hawaii remains steadfast,” the companies said, including maintaining robust service between islands.

“With the additional scale and resources that this transaction with Alaska Airlines brings, we will be able to accelerate investments in our… technology, while maintaining the Hawaiian Airlines brand,” Hawaiian Airlines chief executive Peter Ingram said in the statement.

Federal regulatory approval of the purchase is not assured.

US airlines have faced cutthroat competition in recent years, seeking to consolidate against financial pressure even as they endure federal antitrust scrutiny.

The administration of President Joe Biden last year blocked an alliance between American Airlines and JetBlue Airways, and is seeking to halt JetBlue from buying Spirit Airlines, arguing that consolidation may not favour consumers.