Cables snapped on a lifeboat and it plunged 20 metres (65 feet) to the ocean and fell upside down, killing the five and injuring three others aboard, during the mock rescue exercise on the Thomson Majesty, operated by British travel group TUI Travel plc. The boat was docked in the port of the capital of the island of La Palma, Santa Cruz.

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Safety tests on lifeboats are a significant source of accidents, according to a report by Britain's Marine Accident Investigation Branch.

There were 1,498 passengers on board the 20-year-old ship at the time, a Thomson Cruises spokesman said. None of them was involved in the accident. The ship is registered in Malta and owned by Cyprus-based cruise line Louis Cruises.

"We are working closely with the ship owners and managers, Louis Cruises, to determine exactly what has happened and provide assistance to those affected by the incident," Thomson Cruises, owned by TUI Travel plc, said in a statement.

Three of the dead were Indonesians. The other dead were a Filipino and a Ghanaian. Three more crew members were injured. One person has been discharged from hospital and the other two people were expected to be released from hospital imminently, the company statement said.

In Britain, the general secretary of the RMT shipping union, called for better safety standards.

Union leader Bob Crow said in a statement: "The thoughts of all seafarers will be with the friends and families of those who have lost their lives in this tragic incident.

"Once again the spotlight is on the issue of safety in the UK shipping and cruise industry and RMT awaits the outcome of the investigation and recommendations that can prevent any repetition of today's shocking events."

The Thomson Majesty, with five restaurants and two swimming pools, cruises to the Canary Islands, the Mediterranean and the Red Sea, according to Thomson's website.