Italian coastguards and volunteers have been working for three days to cut the net from around the mammal.
An operation to free a sperm whale ensnared in a fishing net off the coast of Sicily entered its third day on Monday.
Coastguards, volunteers from the marine conservation NGO Sea Shepherd and marine biologist Carmelo Isgro have been working to cut the net from around the mammal for more than two days.
Isgro explained on Facebook that the net had wrapped itself around the mammal from "head to tail" and that work to remove it has been slow because the animal is skittish.
"She is very nervous and does not let herself be helped. Last night the sperm whale began to make longer and longer dives (over half an hour for a single dive)," he wrote.
"As she often surfaces away from the dive site, it's not easy to spot her when she returns to the surface and at nightfall, we lost sight of her," he added.
"I assure you that operating with knives on a 12-meter animal that wriggles like a madman in pain and that has the strength to easily move the 15 tons of its weight is not a trivial matter," he went on, praising his fellow divers' "incredible courage".
Divers lost track of the animal at nightfall on Sunday and spent Monday looking for it in vain.
Most of the net has been removed but the whale's tail remains encased, Isgro said. Rescuers hope to be able to spot the whale again on Tuesday.
According to Sea Shepherd, it's the second whale to be caught in an illegally cast drift net over the past three weeks in this area.
"The entire marine ecosystem is under attack by illegal fishing," the NGO wrote on Facebook.