SANTIAGO (AFP) - It was meant to be Chile's first drawbridge, in Valdivia, but was built with at least one traffic deck upside-down, so opening day will have to wait, officials said on Tuesday.

The project was supposed to open this month, and become an instant landmark connecting Valdivia with Teja island by bridging the Cau Cau River.

But it has ended up a laughingstock in local social media, as Chileans wondered how construction workers managed to mess up something as seemingly clear as up and down.

The gaffe also got President Sebastian Pinera a bit defensive.

"It can be fixed... and it will be fixed by the company that made the mistake," Mr Pinera said dropping the ball in the court of Spanish infrastructure builders Azvi.

Inspectors getting ready for opening day found that either one or two of the traffic decks were installed backwards, authorities said, though they presumably know their drawbridges even if the old technology is new to Chile.

"The only responsible party is the builder. We are going to make them answer for this," Public Works Minister Loreto Silva fumed.

Azvi did not immediately comment. And no new opening date was announced.

Valdivia, 840km south of sprawling Santiago, has about 125,000 people.