Around 6,000 poppies, service medals and memorial plaques have been stolen from a Royal British Legion centre.
The items, along with poppy wreaths, crosses, appeal wristbands, Union flags and high-vis jackets used by appeal collectors, were in a 20ft aluminium shipping container.
The container, which was in the grounds of the Royal British Legion at Ordsall District Centre in Salford, Greater Manchester, was taken some time between 4pm last Thursday and midday on Tuesday.
Detective Sergeant Julie Connor, from Greater Manchester Police, said: "The container was very large and heavy and would have required a large vehicle and lifting equipment to remove it.
"The proceeds of the Poppy Appeal are used to support our soldiers in personal recovery centres for injured soldiers, welfare support for serving and ex-soldiers, and those injured while on duty.
"This crime will directly affect those personnel who dedicate their lives to serving our country and it is essential we recover everything.
"I would urge anyone who has any information to the whereabouts of the items and the container, to contact police as soon as possible. Understandably, those at the British Legion have been left devastated by this theft and without the items will not be able to make this year's Poppy Appeal a success."
Anyone with information should phone police on 0161 856 5351 or the independent charity Crimestoppers, anonymously, on 0800 555 111.