The number of illegal immigrants crossing into the United States would surge more than five times the current wave of 90,000 if President Obama grants amnesty to up to 6 million undocumented people as many advocates expect, according to an immigration expert.

“It could hit nearly half a million people,” said Jessica M. Vaughan, director of policy studies with the Center for Immigration Studies. She said that the additional 500,000 would come in the first year following an amnesty plan.