A Danish inventor suspected of killing a Swedish journalist on board his submarine could be charged with murder, a prosecutor said.

Jakob Buch-Jepsen said police expect to raise the preliminary charges against Peter Madsen from manslaughter to murder and indecent handling of a corpse when he appears at a custody hearing on September 5 on whether his pre-trial detention should be extended.

"We will make an ongoing assessment of whether it should happen before," Mr Buch-Jepsen told the BT tabloid.

Police earlier revealed that the headless torso of reporter Kim Wall was found naked and they are now searching for her clothes.

The 30-year-old was last seen alive on August 10 aboard the submarine.

The cause of the journalist's death is not yet known, police said.

The home-made submarine on which police believe the journalist was murdered. Photo: Reuters

Divers and members of the Danish Emergency Management Agency were combing the coast off Amager island in Copenhagen, where Ms Wall is believed to have died, looking for an orange turtleneck blouse, a black-and-white skirt and white sneakers, Copenhagen police spokesman Steen Hansen said.

A cyclist discovered her torso on Monday. Copenhagen police say the body's head, arms and legs had "deliberately been cut off". DNA tests have confirmed the torso was Ms Wall's and dried blood found inside the submarine, which sank during the trip, also matched her DNA.

According to her family, Ms Wall was working on a story about Madsen, 46, who dreamed of launching a manned space mission.

Madsen initially told police he had let Ms Wall off the submarine on an island. He later told police he buried her at sea after an accident aboard his submarine, UC3 Nautilus.

Tabloid Ekstra Bladet, quoting unnamed sources, said Madsen has asked to be transferred to solitary confinement, allegedly out of fear of being attacked inside the prison.