The prison was the main target, but no prisoners escaped, Afghan President Hamid Karzai's half-brother said. Ahmed Wali Karzai, a member of the Kandahar provincial council, said two of the explosions occurred near his home, which was not damaged.
Wali Karzai said that Canadian troops had reinforced the prison with cement block after a suicide attack in 2008 blew apart the prison gates and freed hundreds of criminals and suspected insurgents.
"They wanted to keep people busy in the city and break the prison, but the Canadians last time did a good job," Wali Karzai said. "They did a lot of reconstruction so they couldn't break the prison this time."
One suicide attack struck at the front gate of the Kandahar police headquarters, causing a lot of casualties, he said.
"There are a lot of civilian causalities," Wali Karzai said. "There are houses that have collapsed and businesses and people are still under the rubble. There was a wedding hall near the police headquarters and there was a wedding. A lot of casualties there from the explosions."
He said at least 30 people were killed and another 47 people were injured. Kandahar has a population of 800,000 and is the provincial capital of Kandahar province, the spiritual birthplace of the Taliban movement.
U.S., NATO and Afghan forces are planning an offensive in Kandahar province later this year, a follow-up to an ongoing military operation in neighboring Helmand province. Thousands of troops worked for three weeks to seize control of the district of Marjah from the Taliban.
The Marjah offensive is the first test of top Afghanistan commander, U.S. Gen. Stanley McChrystal's strategy to rout insurgents from areas, set up new governance and rush in development aid in hopes of winning the loyalty of the residents.
Wali Karzai said local intelligence officials were tipped to the attacks in Kandahar.
"I knew a month ago that this might happen," he said. "There were rumors around."
Kandahar Mayor Gulam Hamidi scrambled to send equipment to the explosion sites.
"Several buildings have collapsed, some houses and some shops," he said. "I am sending my equipment to help the police to try to dig through the rubble."
His daughter Ragina Hamidi, who runs a small women's-only business in Kandahar, said she heard one small explosion followed by two larger ones and then a fourth.
"We can hear planes overhead and there is still some firing in the distance," Ragina Hamidi said in a telephone interview.