At around 0710 GMT, the company’s stocks had tumbled 49 percent to HK$2.38 ($0.30, 0.25 euros).
The fall represented a loss of more than 3.5 billion euros ($4.3 billion) for the company, which is headed by billionaire Oleg Deripaska, and which accounts for some seven percent of the world’s aluminium production.
The collapse came after US President Donald Trump on Friday announced sanctions against Russian oligarchs close to Vladimir Putin following the diplomatic crisis sparked by the poisoning of former spy Sergei Skripal.
Washington has accused Deripaska of operating for the Russian government. Other magnates hit by sanctions include Alexei Miller, director of state-owned energy giant Gazprom.
In a statement, Rusal said the sanctions “may result in technical defaults in relation to certain credit obligations of the group”.
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