A powerful car bomb attack on a police bus on Thursday in Pakistan's commercial hub of Karachi killed at least eight policemen and injured at least 36 others, officials said.

The attack came early in the morning. "Apparently an explosive-laden car hit the police bus transporting officials for security duty," Muhammad Iqbal, a senior police official, told Agence France Presse.

Doctor Semi Jamali at Karachi's Jinnah hospital confirmed that they had received eight bodies. At least 36 injured officers were hospitalized, ten 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 50-55 policemen were boarding the bus and going somewhere for duty from their training center," Iqbal said adding that police suspect it was a suicide attack.

There was no immediate claim of responsibility for the attack.