Cows at dairy farms in Texas and Kansas tested positive for a contagious strain of bird flu in an "unprecedented development," Texan farming authorities said Wednesday.

The Texas Department of Agriculture and with other state and national agencies "are working around the clock to ensure the safety of our food supply," said Texas agriculture commissioner Sid Miller in a statement.

But Miller added, "While troubling, this outbreak is not currently expected to threaten our nation's commercial dairy supply."

Texas is among the five largest milk-producing states in the United States, according to data from the US Department of Agriculture.

The press release said that tests had found no alterations to the virus that would make it more transmissible to humans and that the risk to the public "remains minimal."

"Further efforts to continue epidemiological investigations are underway to ensure a complete picture of the situation can be evaluated," it added.

The TDA said positive samples were retrieved from unpasteurized milk collected from two dairy farms in Kansas and one in Texas, with analysis confirming the results on March 25.

It added that HPAI had not been detected in any beef cattle but urged all farmers to implement "enhanced biosecurity measures on their farms and ranches to protect their herds."

The TRA said it was working alongside the US Food and Drug Administration (FDA) and other agencies to evaluate symptoms among primarily older dairy cows in Texas, Kansas and New Mexico.