The Times of London reported police said three of the 25 wounded were in critical condition.
The newspaper said it was Britain's worst mass killing since the Dunblane Primary School massacre in Scotland in 1996 left 13 dead.
The gunman, identified as 52-year-old Derrick Bird, may have made his twin brother David one of his first victims, The Daily Telegraph reported. The report said Derrick Bird, a father of two, was believed to have killed his brother and an attorney during an argument about their mother's will.
Police said the massacre began about 10:35 a.m. with a double slaying and wounding of a third person at a taxi stand in Whitehaven, and continued for 3 hours until Derrick Bird's body was found in a wooded area near the shootings and two weapons were recovered.
After the initial shootings, Derrick Bird allegedly drove down the street, shooting people as he went, including a Gosforth farmer gunned down as he worked in a field, the Telegraph said.
Shootings also were reported in Seascale and Egremont, Deputy Chief Constable Stuart Hyde said.
The gunman apparently wound up in the area's Lake District before crashing and abandoning his Citroen Picasso and taking his own life.
The cabbie was reported to have told colleagues Tuesday night there would be "a rampage" Wednesday, the newspaper said. The report also said he had been turned away from a hospital after trying to get help for his mental condition.
The Sellafield nuclear reprocessing plant in West Cumbria closed its gates for several hours as a precaution but since has reopened, the BBC reported.
Cumbria police Deputy Chief Constable Stuart Hyde said the shooting spree "shocked the people of Cumbria and around the country to the core."
Hyde, who wouldn't get into the motive for the shootings, said more bodies might be found, The Times said.
Derrick Bird, who lived in the village of Rowrah, was described as a quiet and personable man who looked after his elderly mother. But he had a heated argument with colleagues the night before, the newspaper said.
A friend, Peter Leder, told the Times that as he signed out for the night, Bird had said: "See you later, Peter -- although you won't see me again."
The Telegraph said Bird had a .22-caliber rifle and a shotgun.
The newspaper said there were reports indicating Bird summoned people to his car before shooting them at point-blank range. Others said they saw him shooting out the window as he drove down the road.
Prime Minister David Cameron said he would do everything possible to help communities "shattered" by the carnage.
"When lives and communities are suddenly shattered in this way, our thoughts should be with all those caught up in these tragic events, especially the families and friends of those killed or injured," Cameron said.