A 6-year-old British girl was stunned when she went to write a Christmas card — and instead found a desperate plea for help from someone claiming to be a “prisoner” forced into slave labor in China, according to reports.

Little Florence Widdicombe says she spotted the alarming message inside one of the cards that were brought from a London branch of Tesco, one of the UK’s leading supermarket chains.

“We are foreign prisoners in Shanghai Qingpu prison China. Forced to work against our will. Please help us and notify human rights organisation,” read the neat all-caps message inside the card with a cat wearing a Santa hat on front, according to the Times of London.

The London schoolgirl told the BBC that the message “made me feel shocked” as well as “sad” when her parents explained what it could mean.

Florence’s father, Ben Widdicombe, said he initially felt “incredulity” at the message, saying they assumed it was “some sort of prank.”

“But on reflection, we realized it was potentially quite a serious thing,” he told the BBC, saying they contacted journalist Peter Humphrey, who was himself imprisoned there four years ago, as the message had requested.

“There is something about that message hitting home at Christmas … that really does make it very poignant and very powerful,” the shocked dad said.

Tesco on Sunday announced that it was also taking it seriously — halting production and launching an investigation into Zheijiang Yunguang Printing, the Chinese supplier hired to make the cards.

“We abhor the use of prison labor and would never allow it in our supply chain,” the company said in a statement. “We were shocked by these allegations and immediately suspended the factory where these cards are produced and launched an investigation. We have also withdrawn these cards from sale whilst we investigate.”

The company claimed previous audits showed no signs of prison labor being used, insisting it would “immediately and permanently de-list” any supplier that broke the rules outlawing the practice.

Humphrey, the journalist whom the supposed prisoner asked for the message to be forwarded to, wrote the initial story about the card for the Sunday Times.

He contacted his “informal network of ex-prisoners” who confirmed that inmates in the foreign prisoner unit are being forced into mundane manual assembly or packaging tasks.

“They have been packing Christmas cards for Tesco, and also Tesco gift tags, for at least two years,” one ex-prisoner who now lives in the UK after his release from Qingpu last year told Humphrey.

“The foreign prisoners just package the cards. They pick different designs, put them into boxes, seal them and pack them into shipping cartons,” the source told him.