Custodians of the Forbidden City have drawn up secret plans for a three-story museum under the sprawling palace in central Beijing to display masses of imperial artefacts that have never been shown to the public, reports The Independent.

But as news of the plans began to leak, critics said the scheme could weaken the foundations of the city's most famous landmark.

Officials of the Palace Museum Management Office have put five years' work into the plan, which they say will allow them to display for the first time some of the 1,052,653 imperial relics now in low-tech storage, susceptible to the ravages of heat and humidity.

In March Sun Jiazhend, the Minister of Culture, declared that a £24m plan had been approved to renovate some of the compound's more dilapidated sections and 'rekindle the brilliance of Emporer Quianlong's golden age - the 18th century height of the Qing Dynasty. But he neglected to mention the underground museum plans.'

The Chinese magazine Southern Weekend, exposed the scheme, warning that it would compromise the soundness of the imperial halls above.