Aug 21 (Reuters) - Donald Trump told a rally at an Alabama football stadium on Friday that he would crack down on illegal immigration if elected president, a familiar theme for the real estate mogul as he seeks the Republican nomination.
Trump, who has rocketed to the top of the Republican presidential pack in opinion polls, told the crowd he wanted to change the constitutional amendment that allows children born to illegal immigrants in the United States to automatically become American citizens.
"Very few places do it. We're the only place just about that's stupid enough to do it," Trump said.
He also reiterated his vow to build a wall along the southern border to stop illegal immigration from Mexico.
The former reality TV star moved his rally in Mobile from its scheduled venue in a hotel ballroom to a more than 40,000-seat football stadium to accommodate the anticipated crowds.
The campaign and local officials had said they expected more than 30,000 people, but media estimates put the crowd at closer to 20,000.
Trump's immigration stance was endorsed by Republican Senator Jeff Sessions of Alabama, who told the crowd, "I'm really impressed with your plan."
Trump has made immigration a central plank of his campaign to win the White House in the November 2016 election. He has said he would deport all undocumented immigrants and rescind US President Barack Obama's executive orders on immigration.
The billionaire businessman began his campaign in June by saying Mexico is sending its criminals and rapists to the United States. The comment sparked outrage from Hispanic civil rights groups and others.
Trump widened his lead over his closest rivals in the past week, a Reuters/Ipsos poll showed on Friday. Nearly 32 percent of Republicans surveyed online said they backed Trump, up from 24 percent a week earlier, the opinion poll found.
Trump had nearly double the support of his closest competitor, former Florida Governor Jeb Bush, who got 16 percent.
Alabama is one of several Southern states receiving greater attention than usual from the Republican candidates because they will host a joint Southern primary on March 1. Tennessee, Arkansas and Texas are among the states also slated to hold primaries that day.The first Southern primary is scheduled for Feb. 20 in South Carolina.