Kentucky has pulled potential tax credits for a proposed Noah's Ark-based theme park, telling the developer on Wednesday that the plans had evolved from a tourist attraction into a ministry seeking to advance religion.

State tourism officials had given preliminary approval for tax incentives of potentially more than $18 million over 10 years for the Ark Encounter park slated to open in 2016, but later warned the park's parent company, Answers in Genesis, that it could lose them if it hired only people who believed in the biblical flood.

Answers in Genesis, or AIG, the organisation behind Kentucky's "Creation Museum," asks employees to sign a faith statement including a belief in creationism and the flood.

The park in Williamstown, Kentucky, is not hiring anyone yet, but a lawyer for the project demanded on Monday that the state drop its requirement that jobs be open to anyone.

Kentucky Tourism, Arts and Heritage Cabinet Secretary Bob Stewart told the project's lawyers in a letter on Wednesday that the original development plans had clearly changed and the tax incentives would not be approved.

"It is readily apparent that the project has evolved from a tourism attraction to an extension of AIG's ministry that will no longer permit the Commonwealth to grant the project tourism development incentives," Stewart wrote.

Ark Encounter officials referred questions on Wednesday to Freedom Guard, a non-profit legal organisation representing them. Chief Counsel Mike Johnson said Ark Encounter was considering filing a lawsuit among other options.

"It may come to that as a last resort," Johnson said, adding they expected to make a decision within days.

"We expect the project to continue, but this will be a huge financial loss to the organization," Johnson said.

Ark Encounter's executive president, Mike Zovath, who is co-founder of Answers in Genesis, said in October that withdrawing the incentives based on the organisation's refusal to give written assurances on hiring would violate its rights.

Plans for the park include a wooden replica of the ark as part of a $73 million initial phase that Zovath said in October had been financed through donations and bonds. He said the tax incentives would help fund additional biblical-themed attractions later.