Port-au-Prince.– Even though aid is getting through, Red Cross experts in Haiti say the situation on the ground remains difficult.

With over 150,000 people dead, the Red Cross is working closely with its staff in Haiti to ensure that emergency supplies are delivered to those coping with the disaster in the most efficient way possible, the aid agency said.

A strong aftershock rattled Haiti Sunday night, forcing parts of the region to be evacuated after the 5.5 quake struck. With the area already devastated, the Red Cross is asking for more help. The American Red Cross says the recovery of Haiti will be long.

The Pan American Health Organization said there had so far been no sign of a feared outbreak of contagious disease among survivors camped out in filthy conditions in about 300 makeshift shelters across Haiti's shattered capital, Port-au-Prince. But some complained they were not getting enough aid 12 days after a massive earthquake hit the Caribbean country.

World Food Program officials estimated some aid had reached more than two-thirds of the survivor camps. Haiti's government reported 609,000 persons without shelter in the wider Port-au-Prince area, though the number of people leaving the capital was increasing daily.

More than 130,000 people have taken advantage of the government's offer of free transportation to cities in the north and southwest. The International Organization for Migration said tents were urgently needed in order to move people out of the makeshift encampments and into orderly tent cities once sanitation and security can be provided.