Haiti was struck by a powerful new earthquake early on Thursday morning, shaking already damaged buildings and sending people fleeing into the streets.
The 6.1 aftershock was the largest since last week's 7.0 quake.
The US Geological Survey said the aftershock was centred about 56km northwest of Port-au-Prince, the Haitian capital.
Despite an international aid operation, supplies have been slow to reach survivors and people are fighting for whatever they can get their hands on in collapsed shops.
Al Jazeera's Tony Birtley reports from Port-au-Prince.