Five males suffered burn injuries following an explosion on Hick Lane in Batley on Wednesday.
Officers were called at 6:47pm (6 February) to Hick Lane and emergency services including ambulance and fire service were quickly deployed to the scene.
The men aged between 35 and 39, suffered burn injuries and were quickly taken to hospital for urgent medical treatment. They all remain in hospital at this time.
The bomb squad were also called to the scene “as a precautionary measure” Police said.
A Royal Logistic Corps bomb disposal van was at the scene on Thursday morning, along with police, fire service and gas vehicles, but has since left.
A police cordon remains in place in Batley town centre whilst enquiries continue to establish the cause of the explosion.
West Yorkshire Police initially believed it to be a gas explosion, but is now treating it as “unexplained”.
“At this stage, we are not treating it as a terrorist incident,” a spokesman told BBC
Drivers are asked to avoid the area and find alternative routes.
Detective Superintendent Pat Twiggs said: “Police and partner agencies have worked throughout the night to ensure the scene is safe and there is no safety risk to members of the public.
“All injured parties are still in hospital receiving treatment for their injuries.
“We will be continuing with our enquiries throughout today and would like to thank the local residents and public for their patience whilst we establish the full circumstances of the incident. At this stage, we are not treating it as a terrorist incident.”
Anyone with any information is asked to call the police via 101 quoting log number 1589 of 6 February.