A Texas state law banning abortion from as early as six weeks into pregnancy has come into effect overnight following inaction by the US Supreme Court on emergency appeals to block it from abortion providers in the state.

The bill dubbed ‘Heartbeat Act’’, was signed into law by Republican Gov. Greg Abbott in May, it prohibits abortions once a foetal heartbeat is detected – something medical authorities say is misleading.

The law will effectively outlaw at least 90% of the abortions sought in the state, according to opponents of the law, since that point is around six weeks into the pregnancy, before some women even know they’re pregnant.

Rights group including Planned Parenthood and the American Civil Liberties Union (ACLU)h says that up to 90% of abortions in Texas take place after six weeks of pregnancy, described the development as “blatantly unconstitutional”.

The US women’s health group Planned Parenthood also condemned the ban, tweeting: “No matter what, we aren’t backing down and we are still fighting. Everyone deserves access to abortion.”

The Supreme Court still has the power to overturn the ban at a later stage.