The 14-inch wide pipe is adjacent to a playground at the Shahjahanpur Railway Colony in Dhaka.
Until 9pm Friday, fire-fighters made five abortive attempts to bring the boy, 'Jihad', up using rope.
Fire Service official Maj Shakil Newaz, who is overseeing the rescue efforts, said they uprooted another 350 feet long pipe, three inches in diameter, that went inside the first one using a crane and created more space.
A team from BUET's mechanical engineering department has arrived at the scene with an alternative plan to save the boy.
After consulting them, Fire Service and Civil Defence Director General Ali Ahmed Khan told reporters that they would try the BUET team's plan.
One of the team members, BUET student Tanvir Arafat Dhrubo said they planned to use another pipe, smaller in diameter, which would have a 'catcher' at the end.
After it reaches Jihad, the mouth of the 'catcher' would open up and get a hold of boy and bring him up, he said.
The work to build the 'catcher' has started near the scene.
Meanwhile, the Directorate General of Health Services has kept a medical team stand by at the spot to meet Jihad's emergency needs once he is rescued.
Director General Deen Muhammad Nurul Haque around 11:30pm told bdnews24.com that the team from Dhaka Medical College and Hospital with a fully equipped ambulance was there to meet the boy's all medical needs.
A little earlier, rescuers planned to send one of their men down the pipe, but it was later dropped considering safety issues.
Nine hours after Jihad fell, Dhaka WASA sent a waterproof camera to get visual inside the pipe. The camera was supposed to be used soon.
Fire Service official Maj Shakil Newaz is leading the rescue efforts.
People across the country are praying for the trapped boy while watching live broadcast of the events unfolding at the Shahjahanpur Railway Colony playground on TV.
Police were having trouble with the large number of onlookers gathered there.
Rescuers said they spoke to the boy several times and provided him with some food, bottled milk and fresh oxygen.
They also sent a torch down the pipe as the evening fell. But Jihad has got weaker after spending long hours in the cold, dark and damp underground.
His father Nasiruddin works as a security guard at the Motijheel School and College. They live in the same colony.
He told reporters that Jihad fell inside the pipe around 3:30pm while playing with his friends. Jihad did not see the pipe as its mouth was covered with a sack.
Three units of firefighters arrived at the scene around 4pm and started the rescue efforts.
But their attempts to save Jihad were facing obstruction as the hole was not that wide.
Jihad had managed to get his hands on the rope four times, but not long enough for the rescuers to reel him up.
Then after 9pm, rescuers uprooted the narrow pipe to create more space.
Residents said the deep tubewell was declared abandoned when it stopped delivering water. A new deep tubewell and pump were being installed near it by the Bangladesh Railway.
Nasiruddin's colleague Abdul Khalek, who had been helping in the rescue attempts from the beginning, said the pipe was 14 inches wide for a specific length underground. Then there were a pump and a filter.
After that, according to him, the pipe is three inches wide and has gone over 300 feet underground and Jihad is sitting on that pump.
Locals said another child nearly had a similar accident on Thursday in the same pipe where Jihad fell. One of the child's legs went inside the pipe accidentally, but the locals saved him.
Jihad is the youngest among his parents' three children. His mother Khadiza Begum, struck by grief, was sat speechless in their house.
Shahjahanpur Police Station OC Mehedi Hasan said the huge gathering of onlookers was hindering the rescue.
State Minister for Home Affairs Asaduzzaman Khan Kamal, WASA Director General Engineer Taksim A Khan, DMP Commissioner Benazir Ahmed, BNP Standing Committee member Mirza Abbas and Dhaka University Vice-Chancellor AAMS Arefin Siddique visited the scene.