More than 100 passengers from a ship at the centre of a virus outbreak began their journey home by train today.

But hundreds more people have chosen to stay on board the Marco Polo and sail to the south of England.

The ship has been berthed in Invergordon, Easter Ross, since Monday after just under 400 people caught a vomiting bug.

Its round-Britain cruise was halted earlier this week and the ship is expected to set sail later today for Tilbury, Essex, where it began its journey.

Passengers were given the option of staying on board or leaving on a specially-chartered train from Inverness.

The train operator said 120 passengers caught the train, which left at 10.15am today.

It will travel to London Kings Cross via Newcastle, York, Doncaster and Peterborough, and will be followed by a coach transfer to Tilbury.

Simon Pielow, the managing director of Train Chartering, said everybody on board the train was "extremely well".

He said: "It's gone extremely smoothly. We were alerted to a request for a train with 700 seats on Tuesday afternoon and we provided that."

The ship's operator Transocean Tours said the Marco Polo is expected to set sail at around 10pm this evening and is due to arrive in Tilbury on Saturday.

Passengers and crew showing symptoms of norovirus have been treated on board the ship.

Transocean Tours, of Bremen, Germany, said the decision for the ship to terminate its 10-night cruise a few days into the trip was taken after it consulted NHS Highland.

Those passengers who doctors think should not travel will remain on board for continued nursing and will be sent home once recovered.

NHS Highland said today that three people remain in Raigmore Hospital, Inverness, after falling ill, while three others have been discharged.

Passenger Roy Sillett, 74, from Norwich, died on Monday of an apparent heart attack which the company said was not related to the bug.

NHS Highland said Mr Sillett had serious underlying health problems.

Transocean said it was unable to comment on reports that the authorities did not know that people were taken ill on its last cruise.

According to the London Port Health Authority, the master of the liner did not inform it of the illness on a cruise to Iceland, which ended last Saturday.

Transocean previously said that a "very small" number of people on Marco Polo's previous cruise had symptoms of gastroenteritis but this was unrelated to the current outbreak.

The company said the ship was given a clean bill of health on returning from its Iceland cruise.

NHS Highland said that around 340 passengers and 40 crew members on board the Marco Polo had symptoms of the illness.

The health board is awaiting results of tests to confirm whether the bug is the norovirus.

When news of the outbreak emerged, there were 769 passengers and 340 crew on board.

The norovirus is also called the "winter vomiting disease" because people usually get it during the winter months but it can occur at any time of the year.

It spreads very easily from person to person and can survive for several days in a contaminated area.

NHS Highland said later that tests confirmed the bug was norovirus and that more than 400 people from the boat were infected.

The information had been shared with the relevant authorities, the NHS board added.