A law in Texas banning abortions after six weeks of pregnancy has taken effect as the US Supreme Court did not act on an emergency request by pro-abortion rights groups to block the measure.

Abortion rights advocates said the law represents the most dramatic restrictions since the Supreme Court’s landmark Roe v Wade decision, which legalised abortion across the country in 1973.

The Texas law, which was signed in May after passing the state’s Republican-controlled legislature, would prohibit 85 percent of abortions previously conducted in the state.

Advocates have argued that women commonly do not know they are pregnant at that point.

At least 12 other states have enacted bans on abortion early in pregnancy, but all have been blocked from going into effect.