(RNS) U.S. religious groups are mobilizing relief efforts for Haitians devastated by Tuesday’s (Jan. 12) massive earthquake, even as they assess the damage to their local partners and congregations.

With many power and phone lines destroyed, U.S.-based aid workers said it is difficult to determine the scope of destruction left by the earthquake and aftershocks that struck near the Haitian capital, Port-au-Prince, at about 5 p.m. local time.

“The communications are still very difficult, very spotty,” said Donna Derr, emergency response director for Church World Service, in a statement.

Haitian President Rene Preval told the Miami Herald that the death toll is “unimaginable” and estimated that thousands have died. Millions more need emergency aid, Preval said.

The Roman Catholic archbishop of Port-au-Prince, Joseph Serge Miot, was among those killed, according to The Associated Press, and two Catholic aid workers from Connecticut are believed to be trapped in the rubble. Four people were killed while attending an Episcopal church service in Trouin, about 20 miles south of Port-au-Prince, according to Episcopal News Service. Both the Catholic and Episcopal cathedrals are badly damaged, according to reports.

“Even under `normal’ circumstances, Haiti struggles to care for her 9 million people,” Episcopal Presiding Bishop Katharine Jefferts Schori said in a statement. “The nation is the poorest in the Western Hemisphere, and this latest disaster will set back many recent efforts at development.”

The U.S.-based Episcopal Church counts Haiti among its 110 dioceses.

Because of Haiti’s long-standing natural and man-made problems, a number of relief groups have offices stationed in the Caribbean nation. “Many of us already have a local presence in Haiti,” said Maurice Bloem, deputy director for Church World Service, “The challenge here is that everybody is still trying to assess its own immediate damage.”

Karel Zelenka, an aide for Catholic Relief Services in Haiti, told CRS headquarters that “people have been screaming and praying all over the place throughout the night. It is a disaster of the century, we should be prepared for thousands and thousands of dead and injured,” according to a letter CRS made public on Wednesday.

Bloem said relief agencies should coordinate their response to the devastation, so as not to overlap efforts and overwhelm Haiti’s fragile infrastructure.

“The last thing Haitians need is another earthquake brought on by aid agencies storming over,” he said.