Traffic froze and construction workers downed tools, while in Beijing's Tiananmen Square thousands gathered, heads bowed, for a solemn military ceremony.
The BBC's Michael Bristow in Beichuan reported that vehicles across the city sounded their horns to mark the event.
Rescue workers laid wreaths outside the town school, resuming their work immediately after the silence.
Trading at stock exchanges halted while the silence was observed.
China has also suspended the Olympic torch relay during the three-day mourning period.
Offers of help in the relief effort from home and abroad have now surpassed $860m (£440m), Chinese officials say.
The first aid supplied by the US has arrived, with an air force plane loaded with tents, lanterns and 15,000 meals landing in Sichuan's provincial capital, Chengdu.
But on its website, China's foreign ministry appealed to the international community for more tents, in what correspondents say is an indication of the magnitude of the problems faced in housing the homeless.
However, a British rescue team standing by in Hong Kong is returning home after being refused permission to travel to the earthquake zone.
There are still stories of survivors being pulled from the rubble.
A week on from the earthquake, an elderly woman was rescued in Beichuan county suffering from an infection and many broken bones, state media said, while another was extracted from a collapsed residential building in Deyang city.
But other stories illustrated how hopes for those still trapped are fading fast.
Video pictures emerged of a man wedged under fallen masonry. He was still alive, and was lent a phone to speak to his wife.
Rescuers later managed to extract him, but not in time to save his life.
Persistent rain is compounding the misery for millions of people made homeless by the quake.
And the weather may deteriorate, with rains turning torrential later in the week, potentially triggering landslides, Chinese forecasters said.
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