CHENGDU -- After a flight of more than 20 hours, Mei Lun and Mei Huan, the first pair of surviving giant panda twins ever born in the United States, arrived at Chengdu early Saturday morning in their first trip to China.

Breeders with the Chengdu Research Base of Giant Panda Breeding, the zoo's Chinese partner, and a throng of panda-lovers greeted the three-year-old bears at Chengdu Shuangliu International Airport around 5 a.m.

Expert Lan Jingchao with the base said the twins would not meet the public immediately until a month-long quarantine check to ensure their health was completed.

Born on July 15, 2013, the twins got their names meaning "something indiscribably beautiful and magnificent" through an online vote.

They are the fourth and fifth offspring of Lun Lun and Yang Yang who came to Zoo Atlanta in 1999 under a collaboration agreement between China and the United States.

Lun Lun has so far produced seven cubs in five births. As part of the agreement, panda cubs born in the United States to parents on loan from China are to be returned to China when they are of age.

Giant pandas in Chengdu have visited 13 countries and regions in total, including Germany, Japan, the Republic of Korea and Mexico, and gave births to 27 cubs overseas.

The Chengdu Research Base is also conducting technical cooperation with their peers in five countries, the United States, Japan, Canada, France and Spain.