The popular rock creation was featured in a number of films and TV shows, including as part of the Gozo island in Game of Thrones more recently. "Reports commissioned over the years indicated that this landmark would be hard hit by unavoidable natural corrosion".
The news was described as "heartbreaking" by Prime Minister Joseph Muscat in a tweet sent shortly after the collapse this morning.
According to the images of the Maltese army, only the cliff remains: the pile and the bridge of the arch have disappeared.
"There was a big raging sea beneath the window", Roger Chessell, a local resident who witnessed the window collapsing, told the Times of Malta. "Suddenly, the ark collapsed into a great clatter, causing an huge sheaf of water".
The Dwejra area, in which the Azure Window was located, is a natural depression produced by the dissolution of subsurface salts which triggered the formation of large circular sinkholes, inlcuding the Inland Sea. "Suddenly, the arch collapsed into the sea".
"That sad day arrived", Muscat tweeted.
The collapse of the Azure Window was not expected imminently, however, Malta leaders said. "By the time the spray had faded, the stack had gone too".
"The Azure Window's demise should serve as an eye-opener to all concerned to look after and maintain and protect where possible, the touristic sites this little island has to offer", the Gozo Tourism Association said in a statement.
Geologists have long warned that erosion from the water would at some point lead to the arch's destruction, and Environment Minister Jose Herrera said no man-made intervention could have stopped the collapse, the Times said.