"Here we go again," US District Judge Carlton Reeves wrote in his order on Friday. "Mississippi has passed another law banning abortions prior to viability."

His new order stops the law from taking effect on July 1. Judge Reeves is the same judge who struck down a 2018 Mississippi law to ban abortion at 15 weeks.

Mississippi is one of several US states that have pushed this year to enact bans on early abortions.

Opponents of abortion are emboldened by new conservative Supreme Court justices and are looking for ways to challenge the court's 1973 ruling that legalised abortion nationwide.

Reeves heard arguments Tuesday from attorneys for the state's only abortion clinic, who said the law would effectively eliminate all abortions in Mississippi because cardiac activity is often first detectable when many women may not know they are pregnant.

Lawyers with the state attorney general's office said the law should be allowed to take effect because it is not a complete ban on abortion, but rather a limit on when the procedure could be done.

Alabama's Republican governor recently signed a law to ban most abortions. Georgia, Kentucky, Louisiana, Mississippi and Ohio have enacted or neared approval of measures barring abortion once there's a detectable fetal heartbeat.

Missouri lawmakers approved an eight-week ban. All of those laws are expected to face legal challenges, and the Kentucky one was temporarily blocked by a federal judge in March.

Reeves ruled last year that Mississippi's 15-week ban is unconstitutional because it would prohibit access to abortion before a fetus could survive outside the pregnant woman's body. Viability is generally considered to be about 23 or 24 weeks.

Also during the hearing, Reeves criticised Mississippi lawmakers for passing an earlier ban after he struck down the one at 15 weeks.

"It sure smacks of defiance to this court," he said.

The state is appealing Reeves' ruling on the 15-week ban, and Republican Governor Phil Bryant signed the new law in March. The state's only abortion clinic, Jackson Women's Health Organization, quickly sued the state.

Bryant said in a statement Friday that he is disappointed in Reeves' ruling.

"As governor, I've pledged to do all I can to protect life," Bryant said. "Time and time again the Legislature and I have done just that."

The Mississippi law says physicians who perform abortions after a fetal heartbeat is detected could face revocation of their state medical licences.

It also says abortions could be allowed after a fetal heartbeat is found if a pregnancy endangers a woman's life or one of her major bodily functions.

Senators rejected an amendment that would have allowed exceptions for pregnancies caused by rape or incest.

Australian Associated Press