Voters headed to the polls in the Midwestern US state of Kansas Tuesday to weigh in on the first major ballot on abortion since the Supreme Court ended the national right to the procedure in June.

The vote is heavy with consequences for Kansans, who will decide whether to remove the right to terminate a pregnancy from the traditionally conservative state's constitution.

But it is also seen as a test case for abortion rights nationwide, as Republican-dominated legislatures rush to impose strict bans on the procedure following the Supreme Court's decision to overturn Roe v. Wade.

Turnout was high after polls opened at 7:00 am (1200 GMT), according to poll worker Marsha Barrett, who said some 250 voters had come to the station in Olathe by noon.

"This election is crazy," Barrett told AFP. "People are determined to vote."

Other states including California and Kentucky are set to vote on the issue in November, at the same time as Congressional midterm elections in which both Republicans and Democrats hope to use it to mobilize their supporters nationwide.

In Kansas, the ballot centers on a 2019 ruling by the state's supreme court that guarantees access to abortion -- currently up to the 22-week stage of pregnancy.

In response, the Republican-dominated state legislature introduced an amendment known as "Value Them Both" that would scrap the constitutional right.

On the other hand, activists see the campaign as a barely masked bid to clear the way for an outright ban -- one state legislator has already introduced a bill that would ban abortion without exceptions for rape, incest, or the mother's life.

Activists also complain that the phrasing of the ballot question is counterintuitive and potentially confusing: voting "Yes" to the amendment means abortion rights being curbed, while people who wish to keep those rights intact must vote "No."