A nine-month-old boy has been found dead at a remote roadhouse about 100 kilometres south-west of Karratha in Western Australia's Pilbara.

The baby disappeared from his Broome home in the early hours of Wednesday morning.

He was found that afternoon almost 1,000km away at the Fortescue Roadhouse at Mardie.

An ambulance rushed the boy to hospital but he was declared dead.

A 25-year-old man has been taken into custody and is being questioned by police.

Major Crime officers are travelling to Karratha this morning to investigate.