French police investigating a suspected €10m (£8.7m) ticket fraud scheme at the Louvre museum in Paris have detained nine people, including two members of staff.

“Based on the information available to the museum, we suspect the existence of a network organising large-scale fraud,” a museum spokesperson told Agence France-Presse.

The Louvre, the world’s most visited museum, reported the suspected scam to police which led to the arrests.

Two Louvre employees, several tour guides and one person suspected of being the mastermind were among those being held, according to the Paris prosecutors’ office.

It is the latest crisis to hit the Louvre, which is still reeling from a heist on 19 October, when a gang raided the museum during daylight hours, breaking in through a window and stealing an estimated €88m of French crown jewels in seven minutes, before fleeing on scooters. Four men have been arrested and are under formal investigation, but the jewels have not been recovered.

The museum’s Denon gallery, where its most valuable paintings are displayed, was hit by a water leak on Thursday evening in the room where paintings from 19th century French artist Charles Meynier and 16th century Italian artist Bernardino Luini are displayed. There was no evaluation of damage as of Friday morning.

The Louvre said it was facing a rise in ticketing fraud of different types. In response it had put in place a “structured” anti-fraud plan in cooperation with staff and the police.

Le Parisien reported that the suspected fraud involved tour guides who had targeted groups of Chinese visitors. The guides allegedly brought in visitors by re-using the same tickets several times for different people. Investigators are working to establish whether the network may have brought in up to 20 tour groups a day over the past decade.

The Paris prosecutors’ office said surveillance and wiretaps confirmed repeated ticket reuse and an apparent strategy of splitting up tour groups to avoid paying the required “speaking fee” imposed on guides, the Associated Press reported. The investigation also pointed to suspected accomplices within the Louvre, with guides allegedly paying them cash in exchange for avoiding ticket checks, it said.

A formal judicial investigation was opened last June on charges including organised fraud, money laundering, corruption, aiding illegal entry in the country as part of an organised group, and the use of forged administrative documents.

The Associated Press reported that suspects are believed to have invested some of the money in real estate in France and Dubai. Authorities have seized more than €957,000 in cash, including €67,000 in foreign currency, as well as €486,000 from bank accounts.

In recent months trade unions at the Louvre have launched several days of strikes, demanding urgent renovations and staffing increases, and protesting against a rise in ticket prices for most non-EU visitors, including British, American and Chinese tourists.