In a dual demonstration of China's military might, hundreds of tanks and armored personnel carriers rumbled through downtown Beijing practicing parade formations tonight, and the government announced that its marines have been holding landing drills in the South China Sea as a warning to Taiwan.

The simultaneous military exercises underscore the determination of China's Communist leaders to showcase their power in the face of perceived challenges at home and abroad ahead of the 50th anniversary of the founding of the People's Republic on Oct. 1.

Thousands of spectators lined the Avenue of Eternal Peace to catch their first glimpse of tanks rolling through the Chinese capital since the military crushed pro-democracy protests in 1989, killing hundreds. Parents brought their children to see the army's show of force, a trial run for the massive military parade that will be the centerpiece of the anniversary celebration just six weeks away.

"This shows the Chinese people's aspirations," said Li Bin, 46, a former soldier, as artillery units rolled by. "We're strong now. For our foes, it's a reminder not to look down on China."

The practice parade came as tensions remained high across the Taiwan Strait. Taiwan President Lee Teng-hui has been vilified in the state-run media here as "the enemy of all Chinese people" for asserting on July 9 that ties between Taiwan and China should be considered "special state-to-state relations."

Beijing considered Lee's statements to be a move toward a formal declaration of independence, which it has vowed would be met with an invasion. The United States is committed to the defense of Taiwan by the 1979 Taiwan Relations Act.

The official New China News Agency reported that Chinese soldiers nationwide have been denouncing Lee, and have declared that "no form of separation will be allowed."

It gave no indication of how many soldiers were taking part in the exercises in the South China Sea, but said the troops are "demonstrating their determination to defend the country's territorial integrity, as well as displaying their military strength."

The announcement marked the first time during the latest crisis with Taiwan that the government has officially linked a military exercise to its displeasure with Lee. A number of other military announcements in recent weeks have been interpreted as veiled threats against Taiwan, including Beijing's declaration that it has neutron bomb technology.

In Beijing, the tank formations began pouring in at 7 p.m., blocking many key transportation arteries and delaying many of the city's commuters. Heavier tanks were directed onto bike paths to avoid putting too much weight on overpasses.

"This is so irritating," snarled one woman as she tried in vain to pedal through the gridlocked bike lane along Beijing's main avenue. "I can't get home."

The grinding sound of tank treads rolling on asphalt reverberated through the streets into the early morning hours. Some observers said the spectacle served to send a signal both internationally and domestically.

CAPTION: A policeman keeps an eye on people assembled on Beijing's Changan Avenue to watch military vehicles preparing for the October celebration.

CAPTION: A truck full of troops makes its way along Changan Avenue to Tiananmen Square to rehearse for the full-scale military parade that will mark 50 years of Communist rule of China.

CAPTION: Taiwanese tanks fire practice rounds at a base near Taipei at about the same time that China announced it had been holding landing drills in the South China Sea as a warning to Taiwan.