The prominent sight of the 465 foot (141-metre) multi-deck Nord in the city's Victoria harbour in recent weeks had sparked criticism from the United States' State Department, which questioned the "transparency" of the financial hub and warned of reputational risks.
Mordashov, a billionaire close to President Vladimir Putin, was among a number of Russians sanctioned by the U.S. and European Union - but not the United Nations - after Russia's invasion of Ukraine for their links to Putin.
While a number of Russian superyachts have been seized or denied entry in Europe and other jurisdictions, the Nord was left undisturbed in Hong Kong after its arrival on October 5.
Valued at over $500 million, it arrived via a seven day voyage from Vladivostok in Russian Far East, down through the Sea of Japan and the East China Sea.
The Hong Kong government did not immediately respond to Reuters' questions on Thursday night.
The MarineTraffic site put the vessel southeast of Hong Kong waters early on Thursday evening, heading into the South China Sea.
A Reuters witness saw a fuel barge alongside the vessel inside the harbour at noon.
Hong Kong's leader John Lee said on Oct. 11 that the city's authorities would not act on unilateral sanctions imposed on Mordashov by individual jurisdictions.
"We cannot do anything that has no legal basis," said Lee, who himself has been sanctioned by the U.S. for his role on a crackdown on local freedoms.
Lee, who is due to host an international investment summit in November with global business leaders, said the Chinese-ruled city would only abide by United Nations sanctions.
(Reporting By Greg Torode and Donny Kwok in Hong Kong; Editing by Raissa Kasolowsky)
By Greg Torode and Donny Kwok
