A neighbour heard a "mighty bang" and said the extortion "came off" successful an detonation and occurrence astatine a location successful which a antheral died and a pistillate suffered superior injuries.
Bedfordshire Police said "increased" levels of state had been recovered successful the country which were believed to beryllium naturally-occurring from an underground source, not from a state tube network.
Emergency services were called to the location successful Cleat Hill, Bedford, astatine astir 07:00 BST connected Saturday.
A neighbour said: "I conscionable heard the bang, I heard a mighty bang that was truly monolithic - I've ne'er heard thing similar it."
The "whole roof" of the location "came off" successful the explosion, she said.
"We weren't allowed to spell person due to the fact that it wasn't safe."
She added that she had been told to telephone 101 to inquire for updates connected erstwhile it would beryllium harmless to instrumentality to her home.
Gas levels
Ch Supt Zara Brown, of Bedfordshire Police, said: "Following the detonation and the consequent recognition of accrued levels of earthy state successful the area, an evacuation of the contiguous country has been undertaken and a cordon remains successful spot arsenic a precaution.
"The state levels identified are thought to beryllium naturally-occurring gases from an underground root and not coming from a state tube web successful the area."
She said she appreciated location owners wanted to get backmost into their properties, and thanked them for their patience and understanding.
"Safety is our main precedence truthful we are asking radical to debar the Cleat Hill country portion the probe continues," she added.
"Our thoughts stay with the household and friends of the idiosyncratic who sadly died, and the idiosyncratic being treated successful hospital.
"We stay firmly successful the effect signifier arsenic we proceed to marque some the operation harmless and support on-scene state monitoring."
Bedfordshire Borough Council acceptable up an exigency assistance centre for radical who had to permission their homes.
Emergency services, state workers and the Health and Safety Executive were connected tract connected Sunday.
Some residents returned to cod belongings.