The latest quake in the Rangamati hill district, bordering Myanmar and far-eastern India, was a five-second tremor that hit the village of Barkal Friday, opening up a 10-kilometre-long (six-mile) crack, officials said by telephone.
The biggest quake in the area in the past week was on July 27 and measured 5.09 on the Richter scale. Two women were killed and 25 people injured as houses collapsed in the tremor.
The other earthquakes have been described as mild.
Several hundred villagers have fled the area over the past week fearing another deadly tremor, officials said.
Experts have visited the site to study how to respond to a larger earthquake.
One of them, Chittagong University geography teacher Shahidul Islam, said there were hundreds of cracks in the hills tracts, a sign that a major geological change was under way in the scenic wooded region.
"The region is perched on the earthquake zone," he told reporters after touring the area.
Experts fear a large quake could damage one of Bangladesh's major hydroelectric dams, Kaptai, and have proposed a survey to avert a disaster at the facility in Rangamati.
Cash-strapped Bangladesh lacks modern equipment to monitor tremors.
The increasing number of cracks in ground could also lead to more landslides in a country annually ravaged by floods.
A tremor Wednesday coupled with torrential rains triggered a landslide that left six people dead in the coastal resort district of Cox's Bazar, 290 kilometres (182 miles) southeast of Dhaka.
Bangladesh's coast and offshore islands have been battered by rain for the past week. Some 231 fishermen have been reported dead or missing since July 27 amid huge waves and rain showers in the Bay of Bengal.
Some 85 people died in storms around Bangladesh before the downpour that killed the fishermen, and before that, 62 people died in a heatwave.