A major earthquake rocked Haiti on Tuesday and "catastrophic" casualties were feared although no official reports are currently available.

Magnitude-7.0 quake rocks Haiti

The magnitude-7.0 quake, the strongest ever recorded in the area, collapsed a hospital in a hillside district of Port-au-Prince, according to local media reports.

The presidential palace, buildings of the finance and public works ministries, the parliament building and a cathedral in Port-au-Prince were also damaged.

The earthquake struck at about 4:53 p.m. local time (2153 GMT) and was centered 15 km southwest of the capital city, the U.S. Geological Survey (USGS) said.

The quake was relative shallow with its focus at a depth of only 10 km, said the USGS. It said the earthquake was followed by a tsunami seven minutes later and two aftershocks of 5.9-and 5.5-degrees respectively.

Power supplies were cut off in affected areas and communications were interrupted.

Many buildings were damaged, and frightened people could be seen in the streets -- many were searching for their families and relatives from under the rubbles with bare hands, witnesses said.

"I think it's really a catastrophe of major proportions," Haiti's ambassador to the United States, Raymond Alcide Joseph, told Cable News Network.

The United Nations on Tuesday night confirmed that the Headquarters of the UN Mission in Haiti was seriously damaged along with other UN installations and "a large number of personnel remain unaccounted for."

UN Secretary-General Ban Ki-moon was "very concerned" for the people of Haiti and also for many UN staff who serve in the country, a UN statement said here Tuesday.

"At this time of tragedy, I am very concerned for the people of Haiti and also for the many United Nations staff who serve there," the secretary-general said. "I am receiving initial reports and following developments closely."

The earthquake was also felt in the Dominican Republic, which shares the Espanola Island with Haiti.

The Dominican Republic has asked for assistance to Haiti.

"The information we have is that the situation in Haiti is difficult, so we ask Latin America and all the world to help our neighbor," said Dominican Republic presidential office spokesman Frafael Nunez.

U.S. President Barack Obama on Tuesday offered to assist Haiti the quake in the Caribbean country, which the United Nations said was the poorest in the Western hemisphere.

"My thoughts and prayers go out to those who have been affected by this earthquake. We are closely monitoring the situation and we stand ready to assist the people of Haiti," Obama said in a statement released by the White House.

U.S. Secretary of State Hillary Clinton said in Hawaii that her department is gathering information about the condition on the ground in Haiti, and will do its part in providing assistance.

The Los Angeles County and an international aid group based in the area pledged assistance to Haiti.

The Los Angeles Fire Department planned to send about 60 firefighters to aid in the rescue operations. A local Catholic Relief group member said thousands of people could be killed in the earthquake.

Venezuelan President Hugo Chavez announced several hours after the quake that his government would immediately send assistance materials and a team of 50 relief experts to Port-au-Prince.

The Tsunami Warning Center of the Pacific on Tuesday issued a tsunami alert for Haiti, Cuba, Bahamas and the Dominican Republic, saying potential threats exist for coastal areas within 100 km to the epicenter.

A dozen or so aftershocks have been recorded and USGS experts have warned of more follow-up quakes.