The only son of assassinated Pakistani Prime Minister Benazir Bhutto told hundreds of thousands of supporters on Saturday that he would fight for his party's revival, in an appearance intended to mark the official launch of his political career.

"The fountainhead of our power is the people," Bilawal Bhutto Zardari, 26, told the crowd in the port city of Karachi, Pakistan's financial heart and home to 18 million people.

"If you want to save Pakistan, the only answer is Bhuttoism and the PPP," he said, referring to his Pakistan People's Party.