Inspectors have boarded six cruise ships at two UK ports after "serious concerns" were raised about the welfare of their crews.

Five of the ships are berthed at Tilbury Docks, including the Astoria, which has been detained by surveyors acting for the Maritime and Coastguard Agency (MCA).

The sixth ship is at Avonmouth Docks, near Bristol.

All of the ships are being inspected.

Katy Ware, director of Maritime Safety and Standards and the UK's permanent representative to the International Maritime Organisation, said: "We will always take reports around crew welfare seriously and we have used our powers as the Port State Control authority to carry out this detention so that we can investigate more fully."

The Astoria departed the Mexican city of Manzanillo in mid-February and arrived in Poole in the UK on March 10, shipping records show.

It left Poole on March 14 and arrived in Tilbury the next day, where it has remained throughout lockdown.

The cruise ship Columbus sailed to Tilbury from Malta and the Magellan travelled to the Essex port from Iceland's capital, Reykjavik.

Both have been at Tilbury since April.

The Astor, which sailed from the port of Bremen in Germany, and the Vasco De Gama which travelled from Cape Town in South Africa have both been at Tilbury since May.

The cruise ship Marco Polo has been at Avonmouth Docks near Bristol since March 22, having sailed there from Aqaba in Jordan.

All six of the ships are operated by Global Cruise Lines Ltd, the MCA said.

The firm, which has its head office in the Greek capital of Athens, is "designed to manage cruise ships around the world", its website said.

The MCA said in a statement: "The detention is a preventative measure in line with UK Regulations, in order that a full inspection of the ship related to the Maritime Labour Convention can be carried out before its intended departure.

"It cannot leave the port until the inspection is completed.

"Five other ships in the same company - Global Cruise Lines Ltd - four others based at Tilbury and one at Bristol, are also being inspected.

"Acting as the Port State Control Authority for the UK, the MCA has taken this action following a number of serious concerns which were raised about the welfare of the crew."