A bomb attack in Pakistan’s business capital Karachi killed at least seven people, police officials say.

The blast on Wednesday morning targeted Maqbool Baqir, a senior judge at the high court of the southern province of Sindh, where Karachi is the main city, the police said. Officials said that at least nine people, including Baqir, were wounded in the blast.

The bomb detonated as the judge drove past with his security detail. Baqir was rushed to hospital with critical injuries and his driver was killed in the blast, which took place in the Burns Road area, officials said.

"According to initial information, seven people have been killed," Sindh information minister Sharjeel Memon told reporters.

"I can confirm that Justice Maqbool Baqir is critically injured," Salman Syed, a police official said, adding that nine people in all had been wounded by the blast.

"At the moment we can't determine whether it was a suicide attack or a planted bomb," a senior police official Ameer Sheikh told AFP.

Baqir serves as a judge in special "anti-terrorism courts" set up in Pakistan to pass down quick punishments to convicted "terrorists".

Karachi, a city of 18 million people, contributes 42 percent of Pakistan's gross domestic product (GDP) but is rife with murder and kidnappings and has been plagued for years by ethnic, sectarian and political violence.

Ehsanullah Ehsan, the spokesperson of the Tehreek-e-Taliban Pakistan, claimed responsibility for the bombing.

"We attacked the judge in Karachi as he was taking decisions against Shariah and he was harmful for mujahedeen,'' he told the Associated Press news agency in a telephone call from an unknown location.