Potential new voters in Honolulu City Council District 4 have until 4:30 p.m. Thursday to register to vote in the April 13 special election between Trevor Ozawa and Tommy Waters.

There are 66,128 active registered voters and they don’t need to re-register to participate in the special election. They and others who register by next week are expected to be mailed ballots for the election starting March 22.

The district runs from Hawaii Kai to Ala Moana, including Diamond Head and Waikiki.

The special election was triggered by an order issued Jan. 25 by the Hawaii Supreme Court in response to Waters’ legal challenge of the final results issued by the state Office of Elections the morning after the Nov. 6 general election showing the incumbent Ozawa winning by 22 votes over Waters, a former state representative.

A group of 39 East Honolulu residents, mostly Waters supporters, separately raised a challenge, and the court issued the same order.

District 4 residents who are not already voters may register online at olvr.hawaii.gov by 4:30 p.m. Thursday or mail in a completed voter registration form.

Completed written forms postmarked by the registration deadline will also be accepted. Registration forms are available at all public libraries, post offices or may be downloaded at http://www.honolulu.gov/elections.

Individuals who miss the deadline may also register to vote and vote in-person at Honolulu Hale from April 1 to April 12 from 8:00 a.m. to 4:00 p.m., excluding Sunday. They may also register at city hall on election day April 13 from 7:00 a.m. to 6:00 p.m.

Votes are expected to be counted that night.

City Clerk Glen Takahashi put the estimated cost of the special election at $250,000.

Former city transit official Michael Formby was picked by Council members to hold the District 4 on an interim basis until the election is resolved.