The Iowa Caucus - a first key step for the US Democratic Party in choosing their candidate - fell into chaos as results were delayed by the state's party.
The Iowa Democratic Party said that the delay was due to "quality checks" and "inconsistencies" and not a "hack or an intrusion".
The party said the results, which were expected Monday evening, would come at some time on Tuesday.
But the party came under fire as in some local precincts, people blamed a mobile app that was created to report the results.
Party officials said earlier in the day that an early issue with the app would not hinder the process, the AP reported.
Former US housing secretary Julian Castro, who is a campaign surrogate for Senator Elizabeth Warren said the process was a "complete mess" and not "reliable".
Later confusion, nonetheless, allowed many candidates to claim that they were gaining momentum in the race despite the lack of conclusive results.
"By all indications, we are going on to New Hampshire victorious," said Pete Buttigieg, the mayor of South Bend, Indiana.
Elizabeth Warren, the Democratic Senator from Massachusetts said that the results were "too close to call" and criticised current US President Donald Trump in her speech.
Even though candidates do not gain many delegates from the state of Iowa, the caucus is seen as an important first step in the primary that could hurt candidates that underperform in the state.
"The math that I care most about is the fact that this movement is already something that has shocked the political world," said candidate Andrew Yang, a businessman.
Joe Biden, the former US vice president under Obama, said that his campaign thought it would be close but that they would look towards other early primaries.
"We are in this for the long haul," Biden said.
Many experts criticised the Iowa Caucus process and questioned whether it should be the opening election event of the year.
Larry Sabato, who runs the University of Virginia Center for Politics, tweeted congratulations to "ALL the candidates" joking that they would get a "shiny participation trophy" in lieu of any real results.
In a letter published by NBC News, the candidate's campaign criticised the Iowa Democratic Party, telling them: "The app that was intended to relay Caucus results to the Party failed; the Party’s back-up telephonic reporting system likewise has failed."
Several US media outlets including the AP and NBC News reported that Iowa Democratic Party officials hung up on the campaigns after they asked for information during a heated call to discuss the reporting delays.
The AP later reported that organisers in local precincts did not get to test the mobile app that was meant to report results until hours before the voting began.