A newspaper in Hong Kong said the decision had been made because of the "political risks" of something going wrong with the liftoff, which could take place as early as Wednesday morning local time — or Tuesday evening EDT.
Meanwhile, three finalists vying to be China's first "taikonaut" stood by at a remote northwestern desert base ahead of the blastoff.
"The whole Chinese nation is anticipating this great success," Foreign Ministry spokeswoman Zhang Qiyue said.
Elsewhere, China's neighbors pondered how the launch might change Asia's strategic balance.
An ascendant China has long unnerved others in the region, which has benefited from dramatic economic growth in the world's most populous nation.
The military-linked space program offers special cause for unease: Beijing, which has promoted space travel as a nationalistic endeavor, has also kept its exact activities secret.
"China…is displaying its confidence that it is Asia's No. 1 military power," said Tetsuo Maeda, a noted Japanese military analyst. He predicted no immediate effect on Japan's security, but said the Chinese launch will "inevitably hasten Japan's ballistic missile defense program."
China hopes to become only the world's third spacefaring nation, after the former Soviet Union and the United States.
People's Daily said the craft, Shenzhou 5, had completed its final launch test Monday morning and was "sitting on the launch pad with more fuel being injected" Tuesday. It said top Chinese leaders, including President Hu Jintao, were expected to attend the launch.
The newspaper's Web said the rocket would "most probably" take off Wednesday morning.
The government's Xinhua News Agency has said the "No. 1 astronaut" among the three finalists would make the flight — the strongest indication yet that Shenzhou 5 will carry only one crewman. The craft is expected to orbit the Earth 14 times.
China used to broadcast satellite launches live, but stopped in 1995 after a rocket blew up less than two minutes after liftoff, killing six people on the ground. The government is highly sensitive to the propaganda potential — and the possible public-relations liabilities if problems arise.
On Tuesday, it announced that it would not conduct a live broadcast of the event, as previously planned, People's Daily said on its Web site, citing no reason.
State-run China Central Television would not confirm the reports, including a claim by the South China Morning Post in Hong Kong that China's leaders feared the "political risks" of something going wrong with a mission that's been wrapped in patriotic fervor.
"There might be a live broadcast, or there might not," a CCTV spokeswoman, who refused to give her name, told The Associated Press. "CCTV employees aren't allowed to answer that question."
A successful manned mission would catapult China far beyond its Asian neighbors, many of whom don't have space programs. However, some consider it a victory for Asia in a technological area dominated by Western nations.
"We should be proud of the fact that Asia's space technology has come this far," said Yoon Duk-min, a regional security expert at the Institute of Foreign Affairs and National Security in Seoul, a government-funded think tank.
He said a spacefaring China could inspire healthy competition in space research and "help elevate Asian technology by one significant notch" if Beijing has peaceful intentions.
"If China uses its space technology for military purposes, it could have awesome implications. It could lead to an arms race in the region," said Yoon, who allowed that he considered that scenario unlikely.
One particularly wary neighbor is probably India, whose size approaches China's. The two nations' often tense relationship has involved border disputes and deep mutual suspicion.
"India should be monitoring China's capability," said Uday Bhaskar, the deputy director of the government-funded Institute of Defense Studies and Analyses in the capital, New Delhi. "India and China are natural competitors. The challenge is to keep it healthy."
China has promised its forays into space will be peaceful.
By Joe McDonald