The first explosion, caused by a roadside bomb, was followed by a botched suicide attack believed to have been carried out by a woman.
That second blast also killed another woman believed to be a suicide bomber and injured several pedestrians.
In all, four police officers, a child, and two suspected suicide bombers died in the explosions.
Police superintendent Imtiaz Khan told RFE/RL at the site of the second blast that bomb-disposal squad officials have confirmed the attack was carried out by a suicide bomber.
"There was a blast and we saw a woman fall down," Khan said. "Her chest was blown up while her back was intact. It was a clear-cut suicide attack."
The police officer said the first blast was caused by an explosive device planted on a handcart at the side of the road, and targeted a police van. The blast killed four policemen and injured 16 others.
Eyewitnesses said the first explosion rocked the whole Lahori Gate area and people rushed out of their houses. It was followed by the second, less-powerful explosion.
Injured policeman Ali Sher told RFE/RL that he was on duty when the first blast rocked the area and he was hit by shrapnel.
"They were busy pushing away the crowd from the site of the first blast when there was another explosion," he said. "I did not see what happened as there were so many people, including men and women, there."
The city of Peshawar -- which has a population of some 3.5 million people -- has witnessed a number of suicide attacks and bomb blasts since the beginning of 2011.
The past two months were relatively calm, however, as police officials say they have imposed tighter security inside and outside the city.
with agency reports