People from Doncaster to Sheffield reported hearing several loud blasts in the early hours of last night and this morning - and the explosions were said to be too loud to be fireworks.
But now South Yorkshire Police has confirmed that a number of controlled explosions were carried out at a number of schools in South Yorkshire yesterday to blow up stocks of a dangerous chemical which has been outlawed across the country by the Government.
Schools across Britain have been told to get rid of stocks of 2,4 dinitrophenyl hydrazine (DNP) which has been used in science lessons and lab tests but is now considered dangerous if incorrectly stored.
A force spokesman confirmed that bomb disposal squads visited a number of schools in South Yorkshire yesterday after discovery of the chemicals on premises.
The spokesman said: "A number of schools across South Yorkshire were visited yesterday by Explosive Ordinance Disposal (EOD) specialists, following national concerns about the storage of certain chemicals within the school premises.
"A number of controlled explosions were carried out following those visits. This measure is being taken across the country following a Government notice, to minimise any risk."
No details of the schools involved or the time of the blasts have been released.
Guidance was been issued nationally, with teachers urged to check if laboratories held stocks of DNP and controlled explosions of the substance have already taken place at schools across Britain.
DNP, used in laboratory tests, is known to pose a risk of explosion by shock, friction or fire and is usually stored inside a larger container holding water.
A Ministry of Defence spokesman said expert military bomb disposal teams have been deployed to support the Department of Education.
He said they are helping to "dispose of chemicals which have been incorrectly stored by a number of secondary schools" in the "safest possible manner".
Two large blasts - described as too loud to be fireworks - were reported in the early hours by people living in Sheffield, Doncaster and Mexborough.
The two blasts were reportedly originally heard in Handsworth, Manor and Sheffield city centre in the early hours, with people taking to social media to report the noises.
Facebook user Cheryl Hague said: "A lot of people are talking about hearing two loud bangs in Sheffield during the early hours of today.
"Social media reports suggest they were heard in Handsworth, Manor and city - far too loud to be fireworks."