The first blast struck a vehicle belonging to a US security company, killing four Afghan employees and wounding one person, he said.
|Police officers gather at the site of Thursday's|
blasts in the centre of Kandahar city [AFP]
Nadir Jumaa, an Al Jazeera Afghanistan office employee, was also injured in the blasts.
A third roadside explosion took place at the same site but there was no word on casualties, he said.
Separately, a spokesman for the Taliban in the eastern province of Nuristan said six US soldiers and 20 Afghan soldiers were killed in clashes with the group's fighters on Thursday morning in Camdech area.
However, the office of the Nuristan governor refused to comment on the claim, Al Jazeera said.
In a separate incident on Thursday, a provincial police chief was wounded in an attack that killed one of his bodyguards and wounded another.
The attack occurred in Faizabad, the capital of the northeastern Badakhshan province.
Qari Yousef Ahmadi, a purported Taliban spokesman, said on Thursday that the co-ordinated bombings in Kandahar were planned to hit police responding to the first blast.
The violence came less than a week after Mullah Dadullah, the Taliban field commander, was killed during a US-led operation in neighbouring Helmand province.
The Taliban have warned of "bad consequences" if the government didn't hand over Dadullah's body to his relaives.
Kandahar's governor has said that Dadullah was buried at a secret location near Kandahar.
Also early on Thursday, Pakistani and Afghan troops exchanged mortar and gun fire on their disputed border, days after clashes on the frontier claimed more than a dozen lives, a Pakistani official said.
The two-hour battle erupted after Afghan forces fired a mortar at Pakistani soldiers near the Teri Mangal area in the Khyber tribal district, a Pakistani military spokesman said on condition of anonymity.
"Pakistani forces responded effectively and the exchange of fire continued until 5am local time. There were no casualties on the Pakistani side," the spokesman said.
There was no immediate response from Afghan authorities.
The clash happened near an area where a US soldier and a Pakistani trooper were shot dead on Monday after a meeting, also involving Afghan officials, that was aimed at calming tensions.
Afghan officials meanwhile accused Pakistan of starting clashes in the same area on Sunday that continued into Monday, saying Pakistani troops pushed 4km over the disputed border.
Pakistan denied the charges.
Thirteen Afghans were killed in the fighting, which included rocket fire, Afghan officials said.