The figure is comparable to the daily average arrests in May 2019, the peak of a major surge former president Donald Trump used to justify his immigration crackdown.

In January 2021, Border Patrol caught about 2400 migrants a day at the southwest border.

The rising arrests underscore a growing challenge for President Joe Biden as he seeks to shift to a more humane immigration system, while trying to avoid a surge that would overwhelm it.

Immigrant advocacy groups and some Democrats say unaccompanied children and families are not being released from custody fast enough.

At the same time, Republicans and immigration hawks say the willingness to let in more migrants while asylum applications are being heard encourages more migration from Central America.

"We are weeks, maybe even days, away from a crisis on the southern border," Henry Cuellar, a Democrat whose Texas district abuts Mexico, said on Thursday.

"Our country is currently unprepared to handle a surge in migrants in the middle of the pandemic."

The administration is now taking steps to speed up the processing of families caught at the border and greatly reduce use of family detention centres.

It plans to convert two family detention centres in Texas into facilities to quickly process incoming migrant families and allow their release pending the outcome of cases.

The number of people held in those facilities has dropped significantly since the start of the pandemic.

A third detention centre in Pennsylvania was empty as of last week.

US officials are also hurrying to find housing and speed up releases of an increasing number of unaccompanied children arriving at the border with Biden exempting them from the Trump-era Title 42 policy.

Issued on COVID-19-related public health grounds, the law allows US authorities to rapidly expel migrants caught at the border.

The US Department of Health and Human Services said as of March 4 it had 7700 unaccompanied minors in custody, the most since 2019.

Australian Associated Press