Chilean engineers have been left red faced by a delay in the grand opening of the country's first-ever drawbridge - after they discovered a major part was installed upside down.

The $30million Cau Cau bridge was supposed to open this month as an instant landmark connecting Valdivia, a coastal city in the south of Chile, with the adjacent Teja Island.

But no one will be travelling across for a while, after builders realised at least one traffic deck had been installed upside down.

It's a national embarrassment for the prosperous South American country.

But its president, Sebastián Pi?era, is blaming Spanish developers for the mistake.

'It can be fixed, ... and it will be fixed by the company that made the mistake,' fumed President Pi?era.

Public Works Minister Loreto Silva added: 'The only responsible party is the builder. We are going to make them answer for this'

The bridge has ended up a laughing stock among Chilean social media users, who are wondering how construction workers managed to mess up something as seemingly clear as up and down.

One wag tweeted a scrawly child's picture of a bridge, rendered in coloured pencil, with the quip: 'Leak of the installation plans for the Cau Cau bridge in Valdivia.'

The mistake emerged when inspectors getting ready for opening day found that either one or two of the traffic decks were installed backwards, authorities said.

Azvi, the Spanish infrastructure company behind the bridge development, did not immediately comment. A new opening date has not been announced.

Valdivia, which is 520 miles south of Chile's sprawling capital Santiago, is home to about 125,000 people.