Clinton made the comments Tuesday during a fundraising luncheon for local Boys and Girls Clubs, the Press-Telegram of Long Beach reported.
Putin contends ethnic Russians in Ukraine need to be protected. Clinton said that's what Hitler did when he maintained ethnic Germans outside Germany in places such as Czechoslovakia and Romania were not being treated right and needed to be protected.
"Now if this sounds familiar, it's what Hitler did back in the 30s," Clinton said, according to the newspaper. "All the Germans that were ... the ethnic Germans, the Germans by ancestry who were in places like Czechoslovakia and Romania and other places, Hitler kept saying, 'They're not being treated right. I must go and protect my people.' And that's what's gotten everybody so nervous."
The newspaper quoted Clinton as saying Putin is a man "who believes his mission is to restore Russian greatness."
"When he looks at Ukraine, he sees a place that he believes is by its very nature part of Mother Russia," she said at the private event.
Clinton isn't alone in making the Putin-Hilter comparison. On Tuesday, Canada's Prime Minister Stephen Harper said, "What we've seen is the decision of a major power to effectively invade and occupy a neighbouring country based on some kind of extra-territorial claim of jurisdiction over ethnic minorities. We haven't seen this kind of behaviour since the Second World War."
Sen. John McCain (R-Ariz.) endorsed her comments, saying that he's made a similar point in recent days. "If Putin is allowed to go into a sovereign nation on behalf of Russian-speaking people, this is the same thing that Hitler did prior to World War II. He went into the Sudetenland on behalf of German-speaking people. Went into Czechoslovakia on behalf of German-speaking people. So I’m pleased that Hillary Clinton has commented on it," he said.
Clinton continues her California tour Wednesday with an address at the University of California, Los Angeles.