They said the Bahamas-registered Mona Lisa, whose passengers are mostly German, ran aground in the Irbe Strait, a main route from the Baltic Sea to the port of the Latvian capital Riga.

Attempts to pull it off the sandbank failed.

'A decision has been made to evacuate the passengers,' coastguard chief Hermanis Chernov told Latvian public radio.

A coastguard statement said some of the crew would also be taken off, and all would be taken to the port city of Ventspils, some 37km away.

Of the 984 people on board, some 651 are passengers.

Vessels from the coastguard and border guards had been on standby next to the Mona Lisa in case an evacuation became necessary.

The Mona Lisa, which first came into service in 1966 and has eight decks, is on charter to a German ferry tour operator, Lord Nelson Seereisen, from April 28 this year to Aug. 31, according to the Dutch cruise information website www.nedcruise.info.

The ship is lying about 18 km from the coast. - REUTERS