The U.S. Geological Survey said the shallow quake hit 19 kilometers from Port-de-Paix on the country's north coast. It struck at about 3 p.m. local time on Sunday.
"I feel like my life is not safe here", said nun Maryse Alsaint, director of the San Gabriel National School in Gros-Morne, where several classrooms were severely damaged.
Homes and a hospital were also reported to have been destroyed by the natural disaster. The quake was 7.3 miles (11.7 kilometres) below the surface.
The quake was felt in Haiti's capital, Port-au-Prince, as well as in the Dominican Republic, also located on the island of Hispaniola.
A crisis cabinet has been created to coordinate all emergency responses, Prime Minister Jean-Henry Ceant said in a statement posted to Twitter.
Impoverished Haiti, where many live in tenuous circumstances, is especially vulnerable to earthquakes. Rescue workers have said they are not looking for any more victims.
The tremor damaged the facade of a church in the town of Plaisance and a house next door collapsed, Frantz Duval, a journalist with le Nouvelliste, said on Twitter.
There was damage in the northern sections of the country, President Jovenel Moïse tweeted.
Meanwhile, dozens of people could be seen through debris before hauling away rebar to recycle and sell.
According to local authorities, four people were killed in and around the town of Gros-Morne in the south - including a woman who died from a heart attack suffered after the quake. Parliamentarian Alcide Audne told The Associated Press that two of the deaths occurred in the auditorium.
Images of damaged homes and partially destroyed buildings were circulating on social media, but AFP was not immediately able to confirm their authenticity.
Haitian officials said a convoy bringing food and drinking water was headed to the afflicted zone.
A major worldwide relief effort followed the devastating 7.0-magnitude quake that struck the island in January 2010, leaving more than 1.5 million people homeless.