The Biden administration on Friday urged a federal judge to block the nation's most restrictive abortion law, which has banned most abortions in Texas since early September and sent women racing to get care beyond the borders of the second-most populous state.

But even if the law is put on hold, abortion services in Texas may not instantly resume because doctors still fear that they could be sued without a more permanent legal decision.

That worry underscores the durability of Senate Bill 8, which has already withstood a wave of challenges. US District Judge Robert Pitman of Austin, who was appointed by former President Barack Obama, presided over a nearly three-hour hearing but did not say when he will rule.

The law bans abortions once cardiac activity is detected, which is usually around six weeks, before some women know they are pregnant. To enforce the law, Texas deputised private citizens to file lawsuits against violators and has entitled them to at least $10,000 in damages if successful.