ANKARA: Turkish President Recep Tayyip Erdogan on Thursday inaugurated the fourth-longest suspension bridge in the world, the latest of his pet mega-projects.

The Osman Gazi bridge, which has been under construction since 2013, stretches 2.6 kilometres across the Izmit gulf in Turkey's industrial northwest.

“We should have built it at least 50 years ago but we have done it,” he said at the inauguration ceremony.

The $9 billion project is designed to dramatically cut the travel time between Istanbul and the Aegean city of Izmir from nine hours to three and a half.

It is named after the founder and first sultan of the Ottoman Empire, the predecessor of the modern Turkish republic.

A Japanese engineer working on the bridge committed suicide last year because he felt responsible for a mishap during the construction, an incident that made headlines in Turkey.

Critics have blasted Erdogan's mega-projects as excessive and damaging to the environment, but the Turkish strongman defends them as a symbol of his government's achievements.

Pushing for Turkey to become one of the world's top 10 economies by the 100th anniversary of the republic in 2023, Erdogan has promoted a string of ambitious infrastructure works.

In March he laid the last section of a $3 billion bridge spanning the Bosphorous strait, linking Europe and Asia for a third time.

Named after the 16th century Ottoman Sultan Selim I, the bridge is part of a major Istanbul project that also includes a new airport and a canal to relieve pressure from the Bosphorus.