Separatist rebels went ahead with the vote in defiance of Ukraine's pro-Western government and one announced plans to form their own state bodies and military once results are announced on Monday.
Another said the vote would not split the former Soviet republic straight away, but would give the east greater autonomy and could lead to independence or unity with Russia.
Hollande said the vote was so makeshift it could not even be called a referendum. "I don't want to use the word referendum because there is no point," he said on arrival in Baku, capital of Azerbaijan, which, like Ukraine, was once part of the Moscow-led Soviet Union.
"The only election that counts is the one on May 25," he said in a reference to a planned nationwide ballot to choose a successor to Viktor Yanukovich, the pro-Russian president of Ukraine toppled by unrelenting protests.
Hollande also renewed a threat to launch a new wave of sanctions if the presidential election could not go ahead as planned.
In a joint statement, Hollande and German Chancellor Angela Merkel agreed on Saturday to support, if needed, tougher sanctions on Russia - affecting areas such as energy, defence, financial services and engineering - than European Union leaders outlined at a meeting in Brussels on March 6.