Spanish Queen Sofia, accompanied by Chinese Ambassador to Madrid Lyu Fan, on Friday presided over a symbolic signature of an extension agreement between Spain and China over the loan and conservation project of the giant pandas.

With the agreement, the three giant pandas, which have been kept in Zoo Aquarium in Madrid, will stay in the zoo for another five years until 2023.

Two giant pandas -- Bing Xing and Hua Zui Ba -- arrived at Madrid's Zoo Aquarium in September of 2007, thanks to a 10-year cooperation agreement between the two nations. Their daughter, Chulina, was born on Aug. 30, 2016.

Lyu Fan highlighted the role which the pandas have played to bring closer people of the two countries.

"Pandas are considered the national treasure of China and they represent good friendship and the high-level cultural exchange between China and Spain," the ambassador said.

The extension of the agreement and the attendance of Queen Sofia highlighted Sino-Spanish friendship on the occasion of the 45th anniversary of the establishment of the diplomatic ties, Lyu said.

He expected the friendship between Spain and China to "grow tall like bamboos and to be everlasting".

Jesus Fernandez, representative of Madrid-based Parques Reunidos which operates the Zoo, said conservation projects and collaboration among zoos globally have managed to change the panda's conservation status from endangered to venerable.

He also expressed gratitude to Queen Sofia for "the support, the affection and concern to the animals over the last four decades".

This year also marked the 40th anniversary of the first arrival of the giant pandas to Spain.

Zoo Aquarium in Madrid received the first pair of giant pandas from China in 1978. In 1982, a baby panda, named Chulin, was born, which was the first of its species that was born by artificial insemination in Western countries.