A collection of ukiyo-e woodblock prints by painter Katsushika Hokusai and others is among the valuables trapped inside the capsized cruise ship Costa Concordia on Italy's Tuscan coast, its operator said Thursday.

About 6,000 artworks, including paintings and antiques, passenger valuables and jewelry sold in the ship's stores remain inside the Costa Concordia, raising concerns that they could be stolen by enterprising divers. Costa Crociere said it does not know the value of the items.

The ukiyo-e collection includes 12 pieces by Hokusai (1760-1849), three by Kitagawa Utamaro (1753-1806) and a piece by Toshusai Sharaku, who was active in the late 18th century.

Modern paintings and high-end tableware, such as 19th century Bohemian glass, were also on display in the ship.

The ship is being monitored by the coast guard and other authorities and is off-limits to unauthorized personnel, but with salvage work expected to take until the end of the year, AP quoted an expert as saying the Mafia or unauthorized divers will likely start "treasure hunting."