Hottak said the vehicle bomb detonated in the provincial capital of Maidan Shahr as two busloads of mechanics arrived at the gate to begin their day's work.
But long queues of voters had formed as early as 07: 00 local time (02h30 GMT), the polls opened two hours late.
After the incident, authorities postponed the elections to the Afghan Parliament for today. The number of people who were present at the site at the time of the attack is not clear.
On the first day of the elections, 15 people were killed in a suicide attack in the capital Kabul.
More than half a million people were registered to vote across the province, according to the IEC's media relations office, with women making up roughly 1 in 8 registered voters.Turnout figures have not yet been released.
The Electoral Complaints Commission has received thousands of complaints following three days of voting in 33 out of 34 provinces. But hiccups with biometric devices and voter lists persisted.
More than 2,500 candidates, including mullahs, journalists and sons of warlords, are competing for 249 seats in the lower house.
The election, held up for years amid disputes between political factions over voting rules, is one of the biggest tests of Afghanistan's ability to protect itself since an global security force mostly withdrew in 2014.
An independent monitoring group said voting also was marred by ballot stuffing and intimidation by armed men affiliated with candidates in 19 of the country's 32 provinces that were voting last weekend.
On October 20, Afghanistan held its much-delayed parliamentary elections, the provisional results of which will be announced on November 10 and final ones on December 20.
Taliban spokesman Zabihullah Mujahid said the insurgent group was responsible.