Valuable paintings by LS Lowry have been stolen by robbers who tied up their owner and threatened his family with knives.
The Viaduct is the most valuable of the works taken
Louise Aird, 40, let the gang in to the house at Brackenwood Drive, Cheadle Hulme, thinking it was a post delivery.
Three men, armed with knives, tied her art collector husband Ivan up, in what police said was a "terrifying" raid.
Five artworks, thought to be worth more than £1.5m in total, and Lowry's palette and brushes were taken.
The most valuable works are the Viaduct, at about £700,000 and The Tanker Entering The Tyne, which is worth between £500,000 and £600,000.
The others are a pencil sketches - The Bridge at Ringley and The Street Market.
The value of the palette and paintbrushes is not known, because they are so unique.
The raid happened just before 0800 BST on Thursday morning.
Police have produced an e-fit of one of the robbers
Det Ch Insp Linda Reid, of Greater Manchester Police, said: "This would appear to be a targeted attack by burglars who knew exactly what they were looking for.
"They must have known Mr Aird was an art collector and that he would have the paintings in the house.
"These paintings are extremely valuable to collectors but someone would have to know the right people to sell them on to, I would appeal to any art dealers to look at the e-fit and see if it is anyone they know.
"The brutality these men showed to the Aird family was horrific. They may not have physically harmed them but they were left extremely shaken by the whole ordeal."
An e-fit has been produced of one of the robbers. He was white, in his 30s with a round face and was wearing a fluorescent jacket.
Another was of mixed race and the third was wearing a balaclava.
Police also want information on a light blue estate car or people carrier seen close to the house.