Masterpieces by Rubens and Tintoretto were among 15 artworks stolen to order by masked robbers from a museum in Verona, the city’s mayor has said.

Three men dressed in black entered the Castelvecchio museum in northern Italy at the evening change of guard on Thursday, tying up and gagging the site’s security officer and a cashier before taking the paintings.

Their haul included Portrait of a Lady by Flemish Baroque painter Peter Paul Rubens and Male Portrait by Venetian artist Tintoretto, as well as works by Pisanello, Jacopo Bellini, Giovanni Francesco Caroto and Hans de Jode.

The museum told art investigators the works were worth an estimated €15m (£10.5m), adding that it was likely that the job had been masterminded by a private collector.

“Someone sent them, they were skilled, they knew exactly where they were going,” mayor Flavio Tosi said, adding that 11 of the stolen paintings had been masterpieces while others were more minor works.

Council spokesman Roberto Bolis said the museum had 24-hour security, but the robbery had been planned so that the thieves arrived after the building emptied but before the alarms had been activated. “We don’t yet know if they were armed, or whether they took the security officer’s weapon,” he said, adding that the guard and cashier were in shock and were being debriefed by investigators.

“They tied up the security officer as well and took his keys so they could get away in his car,” he said. One of the men watched over the hostages while the other two raided the exhibition rooms. “It was only once they were able to untie themselves that the alarm was raised,” Bolis added.

Footage from the 48 cameras installed in and around the premises has been handed over to police.