Arizona election officials were working to fix issues with voting machines Tuesday as residents cast ballots across the state in a slew of primary elections.

Local media reported Tuesday morning that a number of polling places were closed because voting machines had not been set up, while others were experiencing problems with malfunctioning equipment.

Maricopa County Recorder Adrian Fontes told reporters his team was made aware of technical difficulties with some machines at about 100 polling locations Monday afternoon before working with a contractor to try to address as many problems as possible. At least four voting sites remained shut Tuesday morning hours before the polls closed.

“This is not a hiccup. This is a serious concern where voters across Maricopa County couldn’t get voting,” Fontes said at a press conference, according to the Arizona Republic.

The Associated Press also reported that the contractor had additionally failed to set some of their machines up on time, resulting in voting station closures.

The high-stake elections being considered by voters Tuesday include the Republican U.S. Senate primary race, which is being contested by Rep. Martha McSally, former state Sen. Kelli Ward, and ex-Maricopa County Sheriff Joe Arpaio.