Rice interrupted a tour of Central Asia to make the unscheduled detour on Wednesday to the Pakistani capital, Islamabad, where the government is struggling to cope with the worst natural disaster in the country's history.
She said she came to "express directly" to Pakistan's president, General Pervez Musharraf, and other leaders that the United States was "touched" by the disaster that claimed at least 23,000 lives.
"The United States, like many other people in the world, has been through natural disasters," she said, six weeks after Hurricane Katrina laid waste to New Orleans.
"Our support is not just for today but tomorrow as well," Rice told reporters at Prime Minister Shaukat Aziz's residence.
"We are not just friends between governments but between people," she said.
Pakistan has been a frontline ally in the US-led "war on terror." It dropped its support for Afghanistan's Taliban overnight after the 11 September 2001 attacks and has since backed the US campaign against Islamic extremists.
Rice said US President George Bush had asked Defence Secretary Donald Rumsfeld to coordinate between the US and Pakistani militaries to help earthquake victims.
Bush had pledged an initial $50 million in aid to Pakistan.
A Pakistani Foreign Ministry statement said Rice told Pakistan the United States would provide "tents and water purification plants to help alleviate the suffering".
"We are not just friends between governments but between people"
US secretary of state
Aziz said Rice and Japanese Senior Vice-Foreign Minister Shuzen Tanigawa, whom he also met on Wednesday in Islamabad, had promised helicopters to help the aid operation.
Aziz said "close to 40 helicopters" were sending relief to
the affected areas.
He said Rice was the highest-ranking foreign visitor since Saturday's earthquake and called the United States "a close and important friend".
Aziz said that international aid pledges had so far accounted for $350 million.