The Hong Kong firm's attempt to sell most of its port operations to a US-led consortium was first announced in March after weeks of pressure from Donald Trump.

The US president has refused to rule out military intervention to "take back" the crucial waterway -- which was handed over to Panama in 1999 -- from alleged Chinese control.

Beijing has criticised the sale of the assets to a group led by giant asset manager BlackRock, opening an investigation into the deal to ensure it is handled lawfully.

CK Hutchinson underlined on Monday that "the transaction would never be carried out in any illegal or non-compliant manner".

Asked about the firm's statement on Thursday, a spokeswoman for China's commerce ministry said that "all parties to the transaction must not attempt to circumvent the review process in any way".

No deal may be implemented without prior approval, He Yongqian said at a regular press conference, warning of "legal liability" in the event of proceeding without authorisation.

"It is hoped that the companies involved will maintain a clear understanding of this and proceed with caution," said He.

The business empire built by Hong Kong billionaire Li Ka-shing is registered in the Cayman Islands and the assets being sold are all outside China.

Beijing's next moves in scrutinising CK Hutchison may also have far-reaching implications on Hong Kong and its role as China's business gateway to the world, analysts told AFP.