(CNN) — A major earthquake struck southern Haiti on Tuesday, knocking down buildings and power lines and inflicting what its ambassador to the United States called a catastrophe for the Western Hemisphere’s poorest nation.

Several eyewitnesses reported heavy damage and bodies in the streets of the capital, Port-au-Prince, where concrete-block homes line steep hillsides. There was no estimate of the dead and wounded Tuesday evening, but the U.S. State Department has been told to expect “serious loss of life,” department spokesman P.J. Crowley told reporters in Washington.

“The only thing I can do now is pray and hope for the best,” the ambassador, Raymond Alcide Joseph, told CNN.