Fire crews were called to Green Lane at around 7.40am this morning (Dec 5) following the blast and subsequent fire.
One home, owned by Housing Association Together Housing, was completely destroyed, with six homes evacuated in total.
Three people were taken to hospital and the fire was under control by around 1pm.
West Yorkshire Police said this evening (Saturday) that a woman suffered severe burn injuries, while a man suffered serious injuries.
Another female received minor injuries in the incident.
Chief Superintendent Sarah Baker of West Yorkshire Police, said: “Officers are working with our partners in the fire service, Calderdale Council, Health and Safety Executive and Northern Gas Networks to investigate this clearly very serious incident in Illingworth.
“The cause of the fire is currently under investigation and efforts remain underway to make the area safe and support residents affected by what has taken place.”
Together Housing said in a statement: "We are aware of and are attending a serious incident at one of our properties in Green Lane, Illingworth.
"We are working with the emergency services and other partners and will release further information in due course.
"Our team are on site and are supporting local residents.
"Any additional residents who need support, please contact us on 0300 555 5560.
"Please avoid the area and follow the direction of the emergency services."
Residents in the area have rallied round in a fundraising effort following the explosion, with people offering to donate clothes and food to the family through local businesses and charities.