Plagued by ever-shrinking space to park its hundreds of thousands of bicycles, Amsterdam opened Wednesday the first of its largest-ever bicycle parking complexes, built underwater in a pioneering engineering project.

The shelter is constructed beneath the Open Haven Front, an access tributary to the city's IJ river, and will be followed by another next to the IJ itself that will open in February.

They will have a combined capacity for 11,000 bikes in the cycling-mad Dutch capital.

"Together the shelters will be the largest in the city," the Amsterdam municipality said, with the Open Haven Front storage able to take 7,000 bicycles and the IJ-side site around 4,000.

Construction started in 2019 and involved draining part of the Open Haven Front next to Amsterdam Central Station.

A time-lapse video posted by the Amsterdam municipality showed how the water was pumped out, the structure built and the area eventually reflooded.

"We have a lot of knowledge and expertise when it comes to water," Dutch deputy infrastructure minister Vivianne Heijnen told AFP at the opening ceremony.

This storage "makes optimal use of the space you have in a small country", she said.

Conveyor belts take cyclists nine metres (30 feet) below ground level, according to wUrck, the architectural firm that designed the ultramodern parking spaces that aim to evoke their oceanic surroundings.

"The cyclist steps into an imaginary oyster with a rough exterior of basalt and natural stone and a smooth, light interior," the firm said in a statement.

"Now you will be assured that you can immediately park your bicycle when you come to Amsterdam station," the city's transport alderwoman Melanie van der Horst said.

There are an estimated 900,000 bicycles in Amsterdam with some 625,000 trips made daily, according to the city's 2021 Bicycle Monitor plan -- and finding proper parking has long been a headache.