Costa Concordia: How could this happen to a modern ship?

Shipping experts say it is unclear why such a modern luxury liner should have hit rocks in well-charted, calm waters.

Investigators will be looking into how the Costa Concordia came to be off course, and why it overturned so quickly.

The Independent's travel editor Simon Calder: "It is unbelievable... that this should happen to a 21st Century ship."