Photos showing a 'monster' cruise ship visiting the remote archipelago of St Kilda have sparked outcry after appearing online. 

The UK’s only dual UNESCO World Heritage Site, and one of only 39 in the world, St Kilda is home to nearly 1 million seabirds, including the UK’s largest colony of Atlantic puffins.

There are no permanent residents on St Kilda today but the main island of Hirta is occupied all year round by the people who work on the military base. National Trust for Scotland (NTS) staff are also resident on the island from April to September every year. 

READ MORE: Grave threat of climate change to St Kilda's seabirds revealed in new study

Earlier this week, images of a cruise ship docked off Hirta were shared on X, formerly known as Twitter, leading some to question the frequency of such visits.

Meanwhile, others expressed concern over how such visits ‘help the climate issues’ on the archipelago, which is situated around 40 miles west-northwest of North Uist in the North Atlantic Ocean.

Responding to the concerns raised on X, NTS said it believes that the visit by the cruise ship was unscheduled. 

They wrote: "This was drawn to our attention by St Kilda's Head Ranger, Sue Loughran. We work with the cruise ship industry to encourage responsible tourism and we limit the number of vessels calling into St Kilda. 

“We also limit the number of passengers who come ashore. The companies we work with agree to our biosecurity procedures and wildlife-watching codes. However, on this occasion, we believe this vessel was sailing past the island en route to another destination.

“It did not land passengers and was not scheduled to visit. We will speak to the company about your concerns and appreciate you flagging this to us.”

The cruise ship in question appears to have been Spirit of Adventure, a  58,000-ton cruise ship operated by Saga Cruises, which departed from Dover on May 9 on a scheduled 14-day 'West Coast Explorer: from Orkney to Ireland' sailing.

The itinerary listed on the Saga Cruises makes no mention of a stop over at St Kilda.

A Saga spokesperson said: “Earlier this week, the Spirit of Adventure passed through the Bay of St Kilda on its planned sailing around the Hebrides. Prior to approaching the area, the ship made the relevant local authorities aware of the scenic sail past.

"Given that this is a sensitive area for wildlife, and having worked previously in the region along with the National Trust for Scotland, the captain took all the appropriate procedures to avoid disruption and any adverse impact.”