Residents are unable to return home immediately after a Second World War bomb found in Exeter was detonated, with the explosion heard for miles.

Devon and Cornwall Police were alerted after the device was discovered on a building site on private land to the west of the University of Exeter campus at about 9.20am on Friday.

Initially, a 100-metre cordon was erected, but this was extended to 400 metres on Saturday at the request of the Royal Navy bomb disposal team.

Around 2,600 properties in the vicinity of Glenthorne Road, including 1,400 university students, were evacuated on Friday and Saturday.

Police warned that a “loud bang” was expected when the bomb was detonated on at 6.10pm on Saturday, but said there was no cause for alarm as the cordon meant there were no health risks to anyone beyond its perimeter.

Speaking after the blast, a force spokesman said: “The 400-metre cordon will remain until further notice, so residents should not return home this evening.

“Devon County Council and Exeter Council have been working to support evacuated residents.”

He added: “Around 400-tonnes of sand was transported to the site of the device, which is at a building site on private land, and walls were erected, initially by the Royal Navy bomb disposal experts, followed by Army personnel from the Royal Logistics Corps, to mitigate the impact of the detonation.

“Trenches were also dug to prevent ground shock.

“Despite these mitigation measures, the impact of the blast has been significant and debris has been thrown at least 250-metres away. The crater is around the size of a double decker bus.

“People can be reassured that there are no concerns regarding the impact of the explosion, which caused a large plume of sand, on public health.

“Safety assessments are being conducted this evening and utility companies, including gas, electric and water, are also carrying out assessments.”

It had previously been expected that residents, the majority of whom are staying with friends and family, would be able to return home on Saturday.

Devon County Council confirmed that visiting friends and family was allowed in such circumstances, despite Covid-19 restrictions.

Exeter University asked students not to return to their residences on Saturday to allow safety assessments to be conducted.

One student, Fran Henderson, 18, was told to pack at 7pm on Friday before being taken to a hotel outside of Exeter at 1am on Saturday.

The politics, philosophy and economics student told the PA news agency that she had been informed it was “most likely” that she would be able to return to her student residence on Sunday.

“The site is about 120 metres away from our accommodation,” Ms Henderson said.

Road closures were put in place between Cowley Bride and Exe Bridges during the incident, with diversions in place and motorists asked to avoid the area.