Turkey's Bosphorus tunnel to open sub-sea Asia link
A railway tunnel underneath the Bosphorus Strait is due to open in Turkey, creating a new link between the Asian and European shores of Istanbul.
Turkey's Prime Minister Recep Tayyip Erdogan has for years championed the undersea engineering project, conceived by an Ottoman sultan in 1860.
Work began in 2004 but archaeological excavations delayed the construction.
Japan invested $1bn of the $4bn total cost of the 0.8 mile (1.4 km) tunnel, designed to withstand earthquakes.
It is scheduled to be inaugurated at 13:00 GMT.'Pharaonic'
The BBC's James Reynolds in Istanbul says that now the tunnel is finished, the Turkish government hopes the new route under the Bosphorus will eventually develop into an important trading route, extending from China all the way to western Europe.
Critics of Mr Erdogan have seen the tunnel as one of his grandiose construction projects for the city where he used to be mayor.
Detractors of his proposals, including a third airport, a parallel canal and a third bridge over the Bosphorus, say they illustrate Mr Erdogan's "pharaonic" ambitions.
Authorities came under fire earlier this year when protesters opposed plans to redevelop a park in Istanbul. Widespread violence between anti-government demonstrators and security forces ensued.
The rail tunnel will not be fully operational after its official opening on Tuesday, the news agency AFP reports.
"The part that is in service is very limited. All that has been delayed until much later," said Tayfun Kahraman, president of the Istanbul Chamber of Urban Planners.
"We are wondering why this inauguration is happening so soon."
Japan's Prime Minister Shinzo Abe will be present at the official opening in recognition of the Bank of Japan's status as the project's principal financial backer.
City officials say the tunnel will relieve pressure on the two existing bridges, as well as ease traffic congestion and pollution.