Police have ruled out any foul play behind the massive explosion in Moghbazar area at around 7.30 PM on Sunday and said the initial investigation of the site suggests that the blast might have been caused by ''gas accumulation''.

After visiting the explosion site, Inspector General of Police (IGP) Benazir Ahmed suspects that the blast may have been caused by methane gas.

However, no conclusion can be drawn yet before a full investigation, he said while talking to journalists.

“I do not want to make any comment on the matter. We can draw a conclusion after getting the opinions of the experts,” he said.

“When gas cylinders are not properly maintained they can turn into explosives,” Ahmed said.

He said Sunday’s incident was similar to blasts from gas leaks in Shanir Akhra, Narayanganj and other places. The Narayanganj mosque blast in September last year was caused due to gas leakage.

“We haven’t found anything but shards of glass. It smells like methane gas inside. The Fire Service will bring their gas detector equipment and we’ll see if there’s any gas existing inside,” the IGP added.

Authorities suspect the building that collapsed was the epicentre of the explosion as it had a restaurant and a faulty gas line or gas cylinders used by it could be the reason behind the blast.

The blast was so powerful that the shock wave smashed the glasses of nearly a dozen buildings around it.

Seven nearby buildings and two passenger buses were badly damaged in the blast that killed seven people and injured 400, some 50 of them critically, Dhaka Metropolitan Police Commissioner Shafiqul Islam said late Sunday.

The severely injured were sent to Dhaka Medical College Hospital and Sheikh Hasina National Institute of Burn and Plastic Surgery.

The Dhaka Community hospital treated almost 300 victims, AZM Rahmatullah Shabuj, outdoor in charge of the hospital, said, adding that they treated victims who mostly had cuts in their bodies or their heads.

“Most of them had cuts from the glass shards. Many had wounds in their heads,” Sabuj said.

On the possibility of the explosion being deliberate, the Police Commissioner told bdnews, “It doesn’t look like that to me. If that was the case or had a bomb been exploded, people would’ve been ravaged by splinters.'' “I’ve gathered from the fire service personnel that gas had accumulated here,'' he said.

Fire Brigade chief Brigadier General Sajjad Hossain said primary evidence suggested that the explosion was triggered by a leak after the accumulation of gas.

“There were gas cylinders at a restaurant at the ground floor of the building and air-conditioners at a showroom upstairs. There were gas cylinders also at the road construction site at the scene...investigations have been launched,” Hossain said.

Meanwhile, explosives experts said they have found presence of hydrocarbon in the debris of the building.

''We have found presence of hydrocarbon in the debris while doing analysis,'' Engineer Abul Kalam Azad, chief explosive inspector of Department of Explosives, told The Daily Star newspaper.

''There was a restaurant. The building has natural gas lines and cylinder gas. Besides, there were air conditioners also,'' he said.

Asked whether it is accident or sabotage, the chief inspector said, ''We are analysing all possibilities, including gas leakage. It could have happened from electric spark. We won't ignore any of the possibilities.'' According to residents in the neighbourhood, the explosion rocked the part of the city spreading panic while television footage showed broken pillars, concrete and glass shards strewn across the street at the scene in the central part of the country's capital.

“I was on a bus when the explosion occurred. I jumped out of it through a narrow window of the vehicle, initially thinking the bus gas cylinder exploded... never experienced such a big explosion in my life,” 50-year-old Tajul Islam, who received injuries on his waist and complained of hearing impairment due to the explosion, told PTI.

Another witness said he saw a fireball go over his head and the explosion turned everything dark and smoky in his vicinity while pieces of glass started to shower from above.

“The sound was so huge... it scared everyone,” he told a TV channel.

According to witnesses, soon after the explosion the buses and cars crashed into one another and panic-gripped passengers struggled to get out of the vehicles.

Several residents of an apartment building in the area came downstairs following the explosion.

One of them, Mufakar Ul Islam, added: “We are at a distance here. Still, several glasses of our apartment were shattered.''