The five were crossing the area when the powerful explosion occurred, they said, adding that three nearby buildings were also badly damaged.
Police said the workers had placed the gelatin sticks at quite a depth under the road in the impression that it would implode and create a trench.
They said the contractor should have used only excavators to dig the trench, but had instead used gelatin sticks. No warning signs had been put up, nor was the area barricaded before using the explosives, they said.
