A frightening new aftershock has forced more earthquake survivors on to the Haiti capital's streets and sent others fleeing to the countryside, where aid was only beginning to reach wrecked towns.
A flotilla of rescue vessels, meanwhile, led by the US hospital ship Comfort, converged on Port-au-Prince harbour to help fill gaps in still-lagging global efforts to deliver water, food and medical help.
Hundreds of thousands of survivors of Haiti's cataclysmic earthquake are living in makeshift tents or on blankets and plastic sheets under the tropical sun.
The strongest tremor since the January 12 quake struck at 6.03am yesterday, while many still slept. From the teeming plaza near the collapsed presidential palace to a hillside tent city, the 5.9-magnitude aftershock lasted only seconds but panicked thousands of Haitians.
Up in the hills, where US troops were helping thousands of homeless, people bolted screaming from their tents. Jajoute Ricardo, 24, came running from his house, fearing its collapse.
"Nobody will go to their house now," he said, as he sought a tent of his own. "It is chaos, for real."
A slow vibration intensified into side-to-side shaking that lasted about eight seconds - compared with last week's far stronger initial quake that seemed to go on for 30 seconds and registered 7.0 magnitude.
Throngs again sought out small, ramshackle "tap-tap" buses to take them away from the city. On Port-au-Prince's beaches, more than 20,000 people looked for boats to carry them down the coast, the local Signal FM radio reported.
But the desperation may be deeper outside the capital, closer to last week's quake epicentre. "We're waiting for food, for water, for anything," Emmanuel Doris-Cherie, 32, said in Leogane, 25 miles south west of Port-au-Prince.
The homeless in Leogane lived under sheets draped across tree branches, and the damaged hospital "lacks everything", Red Cross surgeon Hassan Nasreddine said.