At least 17 people were killed and more than 100 injured after an explosion struck an office building in the Bangladeshi capital's commercial district on Tuesday, police and medics said.

The cause of the blast remained unclear but fatal building fires and explosions are common in Bangladesh, where safety enforcement is often lax.

The blast shook the lower floors of a seven-storey building in Gulistan, a major hub for wholesale goods in Dhaka shortly before 5 pm (1100 GMT).

Several floors of the building and the side walls were destroyed in the explosion, which sent rubble and splinters flying into crowded streets.

"At least 17 people have died, including two women," police inspector Bacchu Mia told AFP.

More than 112 people were treated for head wounds, fractures and other injuries at the Dhaka Medical College Hospital, hospital director Nazmul Islam told AFP.

"The pattern of the injuries shows that it was a huge explosion," he said, adding that hundreds of doctors and nurses were mobilised.

He said some injured people were also sent to other hospitals in the city.

Even though rescuers got to the scene within seven minutes of the blast, the extent of the damage has hampered their efforts to reach people who may still be stuck inside, according to Fire Department Chief Brigadier General Main Uddin.

"It’s risky to enter the building now," he said. "We needed reinforcements for columns and beams to continue rescue (efforts) on the ground floor and the underground," Uddin said.

"There is still the possibility of people stuck inside the building," he said.

He added that there was no gas line under the building and no sign of explosives.

"We are trying to find the reason (for the blast)," he said.

Anxious relatives crowded the blast site looking for missing loved ones.

A bus driver caught in the blast said 30 of his passengers were injured when his vehicle was passing the building as the blast hit.

"I heard a loud explosion and then I was hit in the head by a flying object," he told reporters.

Another witness said people were trapped on the second, fourth and fifth floors of the building before firefighters arrived and rushed them to hospital.

The country's health minister Zahid Maleque visited the injured in the hospital and told reporters that most of the fatalities were caused by head injuries.

No substantial fire broke out in the building, which housed dozens of warehouses, shops selling bathroom fittings and other commercial spaces.

"Our officers are investigating whether it was an act of sabotage or an accident," Dhaka police commissioner Khandaker Golam Faruq told reporters.

The military also sent its bomb disposal unit, Rashedul Alam, an army spokesperson said.

Explosions and fires due to gas cylinders, faulty air conditioners and bad electrical wiring are frequent in Bangladeshi buildings and factories.

An explosion at an oxygen plant near the southern port city of Chittagong on Saturday killed seven people.

A fire and subsequent explosions at a container depot in the same town in June last year killed more than 50 people.