The attack is the first in Pakistan, apart from ongoing violence in the northwest, since the country held parliamentary elections a week ago.
"The suicide bomber attacked during rush hour. The intensity of the blast was so strong that it lifted the roof off the vehicle," Kamal Hyder, Al Jazeera's correspondent in Pakistan, said from the scene of the attack.
He said that the medical corps usually had less security than other military units.
"Normally, three-star generals have considerable security. It appears the surgeon-general was a soft target for the sucide bomber," Hyder said.
The blast occurred outside an office of the government's national data registration agency on a crowded main road in the city, which is home to the headquarters of the Pakistani military.
"I can see pieces of flesh littering the road and four damaged vehicles," a witness said.
|Pakistani army forces have been trying to limit|
the movement of opposition fighters [AFP]
Police and troops cordoned off the site of the attack, the witness said.
Pakistan has witnessed a spate of bomb attacks since army troops raided the Lal Masjid (Red Mosque) in the capital Islamabad in July, in pursuit of a Muslim leader thought to have links to the Taliban and al-Qaeda.
The government says the attacks have been carried out by fighters loyal to those organisations.
Most of the fighters are based in a remote mountain region in northwest Pakistan, close to the the Afghan border.
Hyder said people are unsure as to who carried out the Rawalpindi attack, which has shaken the relative peace in the major cities since the parliamentary election.
"Everyone is questioning who could have carried out this attack – particularly given the fact that the leader of the Pakistani Taliban has already said that his men will declare a unilateral ceasefire," he said.
Aid workers killed
In a separate incident on Monday, at least four local staff at a British-aid group were killed in an attack on their office in Pakistan's North West Frontier Province (NWFP).
The attackers sprayed gunfire and threw grenades at the office of Plan International, a non-governmental organisation, in Mansehra.
"We have collected four bodies. There are 10 injured," Mohammad Ashfaq, a local co-ordinator for Plan International, said.
Police said the assailants came in two cars and fled the scene after launching their attack.
Plan International said it had closed its operation in Pakistan after the incident.
"Our primary concern is for our staff and the families of those hurt in the attack," Tom Miller, Plan International's chief executive, said in a statement.
"The attack comes as a shock as Plan has deep roots in the Mansehra area and has worked with the community for more than a decade," he said.