The car-borne bomb destroyed the house of a senior counter-terrorism police officer, Senior Superintendent Aslam Khan, who was unhurt in the attack, AFP reports.
He had been threatened by the Al-Qaeda-allied Pakistani Taliban and knew that he was the target, it reports.
The Islamist militant group said it was responsible for the attack and accused Khan of arresting, torturing and killing Taliban members.
Six officers who were stationed as guards were killed in the attack, along with a mother and a girl as they were walking to the girl's school, said Shoukat Ali, a senior Karachi police official, CNN reports.
Khan heads the counter-terrorism unit of the Police Crime Investigation Department in Karachi, investigating Islamist militant cells in the port city of 18 million people, which is a vital hub for Afghan-bound NATO supplies.
"It was a car bomb attack on my house," he said. "I was receiving threats from Tehreek-e-Taliban (TTP). Taliban are involved in this attack."
Several neighbouring houses were also wrecked in the attack, an AFP reporter saw, with four cars being badly damaged and a two-metre (six-foot) deep crater left in front of Khan's home.
"Eight people including six policemen have been killed and several others were wounded," Shoukat Hussain, another senior police officer, told AFP.
"A child and a woman were also killed. It was a car suicide attack."
Khan said he would not be deterred in his fight against the Taliban.
"I have been receiving threats from the Taliban for a long time," the police official said. "I have been defeating Taliban (militants) by arresting them, and will continue until I have last drop of blood in my body," he said, CNN reports.
Aslam added, "I will give (the) Taliban a lesson which even their children will remember forever."
He said he was asleep before the attack and woke up and ran towards the other rooms of the house where he found his family safe.
"This was a cowardly act of Taliban. I am not scared of Taliban. Let me tell you that I will not spare them in future," he said.
A spokesman for TTP, told AFP, it was responsible.
"We claim responsibility for the attack. Aslam Khan has killed a number of our colleagues and also arrested and tortured many more," TTP spokesman Ehsanullah Ehsan told AFP in a phone call from an undisclosed location.
"He was on our hit list and he is still on our hit list," Ehsan said. He also listed off several other officers targeted.
"They will be killed soon," he vowed.