A girl stands in the lobby of the Adelanto immigration detention center, in Adelanto, California, U.S., April 13, 2017. (Reuters)

US Customs and Border Protection (CBP) has confirmed the death of an 8-year-old girl while in their custody in Texas just days after a 17-year-old boy died in their custody as well.

The girl and her family were in custody at the Harlingen detention facility in Texas, and died as a result of experiencing "a medical emergency" but no further details were provided.

In a news release by the CBP, it was stated that “Emergency Medical Services were called to the station and transported her to the local hospital where she was pronounced dead".

Local media say that CBP officials claimed that "the Office of Professional Responsibility" is investigating the girl's death "as is consistent with protocol." Meanwhile, a spokesperson for the Harlingen Police Department was reported as saying that he held no information about the child's death.

This follows mere days after US and Honduran officials confirmed the death of a 17-year-old migrant Honduran boy in US custody in the shelter of Safety Harbor, Florida, after crossing into the US without his family.

The circumstances arrive after Title 42 was lifted on May 11, and when Homeland Security Secretary Alejandro Mayorkas declared that the "border is not open" while thousands of migrants made last-minute attempts to enter the US.

The average number of migrants taken into custody after crossing the border per day has dropped from more than 10,000 to about 4,400, according to the latest government data.

Hundreds of specialist investigative agents and air marshals from the United States Department of Homeland Security (DHS) are being taken away from their day-to-day jobs to assist with border management, according to reports, prompting some employees to object, claiming they are being transferred to menial chores.

The rule change reinstates a decades-old regulation known as Title 8, which permits border crossers to request asylum, as well as tough new criteria that many believe would speed up deportations and punishments.

Washington believes that the new measures, paired with additional legal avenues, would help to curb the massive influx of migrants to the US-Mexico border, where hundreds of thousands have attempted to cross every month in the last year.

Mayorkas stated that people who chose unlawful pathways to enter will face tougher consequences including a 5-year ban on re-entry and criminal prosecution.