An eight-year-old Guatemalan migrant boy died shortly after midnight on Tuesday after being detained by US border agents, US Customs and Border Protection (CBP) said in a statement, the second migrant child to have died this month after being detained at the border between Mexico and the United States.

The boy and his father were in CBP custody on December 24 when a Border Patrol agent noticed the child showing signs of illness, CBP said. The father and son were taken to the Gerald Champion Regional Medical Center in Alamogordo, New Mexico, where the boy was diagnosed with a common cold and fever, and eventually released by hospital staff.

But later that evening, the boy began vomiting and was transferred back to the hospital. He died at the hospital shortly after midnight, CBP said, and the official cause of death is not known.

The father and son were not identified, and the agency statement said it will release more details "as available and appropriate."

It is the second death this month of a migrant child who was detained after trying to cross into the United States through the US-Mexico border. Earlier in December, seven-year-old Jakelin Caal, also from Guatemala, died after being detained along with her father by US border agents.

Caal's wake was held on Monday, Christmas Eve, in her family's village.