Iowa primary in US presidential election
Republican presidential candidate Donald Trump speaks as his wife Melania watches at a caucus night rally in Des Moines, Iowa February 1, 2016 Reuters

Donald Trump, national front-runner for Republican presidential nomination in 2016, was pushed to second place by Senator Ted Cruz in Iowa primary on Monday.

Conservative lawmaker Cruz notched up 28 percent of the vote in the first primary contest in a long process to decide the Republican candidate, while businessman Trump got 24 percent of votes.

Senator Marco Rubio came in at a surprising and strong third place with 23 percent of votes, making him a strong contender for the nomination.

Democratic front-runner Hillary Clinton too was pushed in the Iowa caucus, ending up tied with her chief rival Senator Bernie Sanders.

With 91 percent of the votes counted, the former secretary of state had 49.8 per cent of the vote while Sanders, a self-described socialist, had to 49.5 percent.

"There is now blood in the water for Donald Trump ... Ted Cruz proved he could successfully beat back Trump attacks because he had a great ground game and identified well with evangelical voters," Ron Bonjean told Reuters.

But Trump underplayed the significance of Iowa saying he hadn't been given any chance in the state.

"I was told by everybody, 'Do not go to Iowa. You couldn't finish in the top ten'," he told supporters. "I said I have to do it," the real estate mogul said.

On the Democratic side, the Iowa results are too crucial for Clinton, who lost the primary battle there to Barack Obama in 2008.

While Republican Mick Huckabee, who won Iowa primary in 2012, said he was suspending the race, on the Democratic side Martin O'Malley suspended the campaign after getting negligible support.