The Maltese-flagged Vitaspirit lost control and ploughed into the edifice, reports said. The building's roof and upper floors collapsed and television pictures showed the basement slumping into the water.
![Their guide said he warned the pair about the dangers in the crater [Shutterstock]](data:image/svg+xml;charset=utf8,%3Csvg%20xmlns%3D'http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg'%20width%3D'100'%20height%3D'100'%20data-ring-placeholder%3D'1'%3E%3C%2Fsvg%3E "Their guide said he warned the pair about the dangers in the crater [Shutterstock]")
Such waterside mansions, known as yalis in Turkish, are among the most historic and expensive properties on the waterway that runs through Istanbul and divides Europe and Asia.
The Deniz Haber maritime news agency said that the vessel lost control due to a technical fault which has yet to be specified.
The vessel was extracted from the mansion but the Bosphorus was closed to shipping traffic in both directions as a precaution, NTV television said. There were no casualties in the collision.
The wooden Hekimbasi Salih Efendi mansion was built by Ottoman nobles in the 19th century. It had no permanent residents but was rented out for marriage ceremonies or concerts.
The Bosphorus is one of the busiest shipping lanes in the world and in 2017 it was crossed by some 42,000 military, naval and commercial vessels.
The government says the risk of such accidents shows the need to build its planned and hugely controversial new canal for Istanbul that would take the shipping traffic and lessen the pressure on the Bosphorus.
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![Fiona Beal killed her partner and lied to everyone about what happened to him [Northamptonshire Police]](data:image/svg+xml;charset=utf8,%3Csvg%20xmlns%3D'http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg'%20width%3D'300'%20height%3D'172'%20data-ring-placeholder%3D'1'%3E%3C%2Fsvg%3E "Fiona Beal killed her partner and lied to everyone about what happened to him [Northamptonshire Police]")
