Earlier, the AFP news agency quoted an election official as saying that the polls would be delayed until February to give officials more time to prepare after the unrest that followed Benazir Bhutto's assassination on Thursday.
But with the government facing calls from the US not to put off the vote too long and opposition parties arguing against a delay, the official said the election commission could not hold off longer than that.
In the violence sparked by the killing of Bhutto in a gun and suicide-bomb attack, several polling offices have been damaged and records destroyed, especially in Sindh, the home province of Bhutto and the stronghold of her Pakistan People's Party (PPP).
Yet, the PPP has rejected the idea of a delay, saying it is ready to participate.
Ready for election
Shah Mahmood Qureshi, a senior party official, told AFP news agency: "We are ready for elections and do not want any delay. We demand immediate elections - and on January 8.
"The government should stick to the schedule. If the government delays the election, we will call a central executive committee meeting to decide our future course of action."
Bilawal Zardari, Bhutto's 19-year-old son, has been chosen, along with Asif Ali Zardari, Bhutto's widower, to succeed her as co-chairmen of the PPP.
"My mother always said that democracy is the best revenge," Bilawal said shortly after being anointed her political successor.
Zardari said he was not running in the election and would not be a candidate for prime minister, but mentioned Makhdoom Amin Fahim, the party vice chairman, as a possible candidate.
Tariq Azim, a spokesman for the pro-Musharraf Pakistan Muslim League-Q party, said: "We are also ready for the contest on January 8."
Earlier, he had predicted that the election could be delayed up to four months.
However, the party of Nawaz Sharif, another former prime minister and vocal critic of the government of Pervez Musharraf, Pakistan's president, has said that a "short postponement" would be acceptable.
On Monday, sporadic unrest flared again with protesters firing into the air in the southern city of Hyderabad and throwing stones at police and shops.
Shops were closed in parts of Karachi, while hundreds of lawyers marched in the southern city of Multan chanting slogans against Musharraf including "Musharraf, you killer".
Bhutto's killing has provoked an angry response across the country, with rioters burning shops, banks and cars over the weekend.
At least 47 people have been killed so far.
The election commission said on Saturday that its offices in many districts of Sindh had been burned and voting material including electoral rolls destroyed.
"All records have been burnt. All electoral rolls have been burnt. Offices of all returning officers have been burnt," Kanwar Dilshad said on Monday, referring to 10 offices in Sindh.
Security fears in two northwestern regions have also raised doubts about voting there, the commission said.
Al Jazeera's Sohail Rahman in Islamabad said that ballot boxes, ballot papers and electoral rolls had been destroyed.
"The chief election commissioner wants a detailed report from each of the provincial commissioners to exactly state what state their buildings are in, how much information has been lost or damaged and how long it will take for that to be re-collated," he said.