The closest country's shore patrol or coast guard would be alerted, but also the rule of thumb is to contact the country that the vessel is flagged under and alert them that they have citizens in peril.
American, Canadian, British, Australian, naval forces will protect their citizens on the open seas and assist each other. Those are not exclusive - other countries would assist during pirate attacks.
The UN General Assembly is now taking steps to act globally. (
www.nst.com.my/Current_News/NST/Saturday...5/Article/index_html)
This will be good news for all ocean travelers.