Details about the Parsons Green blast are still emerging, but Scotland Yard had declared a "terrorist incident" within two hours of the first emergency calls.
Investigators will be scouring CCTV and taking statements from dozens of witnesses as they attempt to piece together the lead-up to the explosion.
Pictures circulating on social media appeared to show wires protruding from a bucket inside a plastic carrier bag, but officers have so far said it is "too early" to confirm the cause of the fire.
If there is a device, it will be forensically assessed after being made safe, while police will be urgently trying to establish whether someone attempted to detonate it, and whether they were present at the scene.
Lydia Corbett, the curate at St. Dionis, told Premier it opened its doors to offer hot drinks to people affected by the explosion. She also said the church's vicar, Rev Tim Stilwell, was out in his dog collar near the station offering to help people in need.
However, the church was forced to close because it was within the police cordon.
Corbett said emergency services have handled the situation well.
"It was relatively calm," she said. "The police did a brilliant job, they had everything under control.
"Our most immediate thing is the secondary school on the green, so we're there chatting with the girls who were affected."
London City Mission has encouraged people to pray for emergency services and for the city's leaders.
Joe Sutton from the charity told Premier: "Be praying for our leaders... the mayor of London, that they know how to respond and how to deal with these constant threats that we face as a city.
"We're just praying for the hope of Christ, the prince of peace, that he would replace fear and anxiety in our hearts this morning."
