Port-au-Prince, Haiti (CNN) -- A strong aftershock rocked Haiti on Wednesday morning just as much-needed medical aid was set to reach the earthquake-ravaged nation.

The 6.1-magnitude aftershock was about 6.2 miles deep,with an epicenter about 35 miles (60 kilometers) west-southwest of thecapital of Port-au-Prince, the U.S. Geological Survey said.

It rattled people struggling to recover from the devastating 7.0-magnitude earthquake that walloped the impoverished country January 12, killing at least 72,000 people.

Such a strong tremor can pose significant danger in a nation wheredamaged buildings are teetering precariously. The aftershock was thestrongest to hit Haiti since last week's original quake, the USGS said.

Patients at a hospital near Haiti's airport in Port-au-Princeimmediately started praying as the ground shook like a ship rockingback and forth. They asked for forgiveness and protection, a nurse said.

At least one injury was reported in the moments after the aftershock, which struck at 6:03 a.m. ET.

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The aftershock jolted Haiti as much-needed medical reinforcementapproached offshore in the form of a state-of-the-art hospital aboard aU.S. naval ship.