LONDON (AP) — Search-and-rescue teams have entered the smoldering rubble of a wood mill in northwest England, trying to find four people who are missing after a massive explosion.

The four — three men and a woman — are believed to have been at the industrial site when an explosion Friday ripped through the mill in the village of Bosley, in Cheshire. Firefighters with a sniffer dog entered the site Saturday.

Paul Hancock, chief fire officer for the Cheshire Fire and Rescue Service, says the longer the four remain missing, the more "it is looking more like a recovery than a rescue operation."

Silos were being doused with water to cool down and thermal imaging cameras were looking for temperature "hot spots."

The cause of the blaze is under investigation.