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Twenty-one airlines will be relocated in mid-May at LAX in what airport officials are calling one of the largest terminal moves in the history of commercial aviation.

The changes, announced Tuesday, are a result of the Delta Air Lines move from Terminals 5 and 6 to Terminals 2 and 3 at Los Angeles International Airport. Delta’s relocation to the north side of the U-shaped airport is part of the huge modernization effort at the nation’s second busiest airport.

The 21 airlines will be moved overnight on three dates: May 12, 14 and 16.

The move affects nearly one-third of the airlines that operate out of LAX, with many moving to new terminals and others to new ticket counters within their current terminal.

The airlines plan to complete their relocations overnight, opening the next morning in their new spots, Los Angeles World Airports said in a news release, describing the effort as “a move of airlines never before seen at a major U.S. airport.”

“While moving 21 airlines over three nights is a monumental task, Delta and the LAWA team have been planning and preparing for months to ensure a smooth transition,” airport commission President Sean Burton said in the release.

Delta may be operating from all four involved terminals at some points during the move, the release stated.

During the relocation, passengers are advised to check into their flights online and arrive earlier than normal, ensuring they’ve gone to the correct terminal. Three neon green buses will be available to shuttle passengers between the affected terminals.

In addition to Delta, the following airlines will be moving during the operation:

Air Canada

Allegiant

Avianca

Boutique Air

Copa

Frontier

Hainan

Hawaiian

InterJet

JetBlue

Qatar

Southwest International

Spirit

Sun Country

Thomas Cook

Virgin America

Virgin ￼Australia

Volaris

WestJet

XL France

Details of the move are posted on LAXishappening.com.

Correction: A previous version of this article misstated one of the dates on which the airlines will move.

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