Panama has complained to the United Nations over US President Donald Trump's "worrying" threat to seize the Panama Canal, even as it launched an audit of the Hong Kong-linked operator of two ports on the interoceanic waterway.

Panama has rejected president-elect's threats, but Hong Kong and mainland Chinese companies have much at stake President-elect Donald Trump's threat to retake the Panama Canal to safeguard US national security has raised questions about the possible impact on Hong Kong and mainland Chinese companies operating there.