RIGA -- Rescue workers on Monday evacuated hundreds of passengers and crew from a German cruise ship which hit a sandbank in the Baltic Sea, a Latvian coast guard official said.

Six Latvian naval and coast guard vessels were involved in the operation after attempts to refloat the vessel failed and warnings of bad weather heightened fears for the passengers on the Mona Lisa.

The ship, with 651 passengers, mainly elderly Germans, and about 330 crew, ran aground on Sunday.

"All the passengers and a part of the crew are being evacuated," Hermanis Cernovs, head of Latvia's navy coastguard service, told Agence France-Presse.

"The passengers will be taken to shore, to the port of Ventspils, and then other services will take care of them," Cernovs said. "Everything is alright with passengers at this moment."

The decision to evacuate the passengers was taken after efforts to set the ship afloat had failed and poor weather warnings were issued for the coming days. It became stranded Sunday from as yet undetermined causes.

"The mood among passengers is good and we have had no medical problems," a representative of ship-owner Lord Nelson-Seereisen, who wished to remain unnamed, told AFP.

The passengers would spend Monday in hotels in the Latvian capital Riga before being flown to Frankfurt, she said.

The Bahamas-registered cruise ship is owned by Herbert Fervers operator of Lord Nelson-Seereisen German tour company based in Erkelenz, west of Cologne.

A company representative told AFP Fervers had gone to the ship to be involved in the rescue effort.

The Mona Lisa set sail May 1 from the German port of Kiel on a 10-day tour of the Baltic.

Tow-boats were expected to resume efforts to set the ship afloat following the evacuation. The Mona Lisa ran aground 18 kilometers (11 miles) off the Latvian coast in normal weather conditions.

The ship's captain is a Greek, according to the Baltic News Service (BNS).