A powerful car bomb attack on a police van in Pakistan's commercial hub of Karachi has killed at least eight policemen and injured at least 36 others, SBS reported.

"Apparently an explosive-laden car hit the police van transporting officials for security duty," Muhammad Iqbal, a senior police official, said.

Doctor Semi Jamali at Karachi's Jinnah hospital confirmed that they had received eight bodies from Thursday's attack.

At least 36 injured officers were hospitalized, 10 of whom were in critical condition, she said.

Police said that more than 50 officers were boarding the vehicle at the time of attack, which occurred in the eastern district of Karachi close to the national highway.

"Around 50 to 55 policemen were boarding the bus and going somewhere for duty from their training centre," Iqbal said adding that police suspect it was a suicide attack.

There was no immediate claim of responsibility.

Karachi, a city of 18 million people which contributes 42 per cent of Pakistan's GDP, has been plagued by sectarian, ethnic and political violence for years.

Pakistan has endured a bloody start to the year with 114 people killed in attacks in January.