Counter-terrorism police are investigating reports of suspect packages being found at army careers offices.
Packages have been found at Oxford, Slough and Brighton, while similar packages were found yesterday in Aldershot, Reading and Chatham, the south east counter terrorism Unit said.
Ministry of Defence bomb disposal units have been called, although this is routine with any suspect package.
Detective Superintendent Stan Gilmour, of the south east counter terrorism unit, said: "Because suspicious packages were found at various locations yesterday, notes were sent out to all the army careers offices, as well as the Post Office, asking staff to be extra vigilant and look out for any suspect packages."
A Ministry of Defence spokesman said: "We can confirm that we are aware of security incidents ongoing in Oxford, Slough and Brighton involving armed forces careers offices.
"The relevant police authorities are investigating with military EOD (explosive ordnance disposal) teams in support and any further inquiries should be directed to the police.
"Security advice has been reiterated to our personnel."
Queensmere Shopping Centre, in Slough, was evacuated, a spokesman for the centre confirmed, while St Giles in Oxford was closed.
It is understood a suspicious package was also reported at the army careers office in St Peters Street, in Canterbury, Kent.
Officers have set up a police cordon and shoppers are being told to avoid the area, the Kentish Gazette reported.