Bertide Horace, a community leader in central Haiti, was awoken in the wee hours last Thursday by a phone call from a woman who sounded desperate.

“Pont-Sondé is being invaded by the gang, please send for help,” the caller said, according to Ms. Horace.

At that moment, members of a Haitian gang armed with automatic weapons were rampaging through the town of Pont-Sondé, according to the United Nations, local human rights groups and videos of the attack taken by some residents, shooting anyone on sight and setting homes and vehicles on fire.

When Ms. Horace, who was about 10 miles away in the city of Saint-Marc, arrived with heavily armed police officers four hours later as the sun was rising, she said the streets of the town were strewed with bodies.

“People were coming out of hiding and trying to flee,” she said in an interview. “It was total panic.”

The wounded, she added, were walking around “begging for help.”

The violence, perpetrated by a gang called the Gran Grif, left at least 88 people, including 10 gang members, dead, the U.N. said.