Police set up a cordon around a garage block and a patch of waste ground in Chadwell St Mary after a serious sexual assault.
Two men have been arrested in connection with the incident. Police were alerted after a young woman reported being assualted in an alleyway off Waterson Road at about 9pm on Saturday, February 23.
The victim, who is from East London, is badly shaken but did not need medical treatment.
The two men, aged 18 and 21 from Grays, were arrested on Sunday, February 24 and remanded in custody. The pair are still in police custody while enquiries continue.
The cordon stretches around the back of some lock ups and a power sub station off Vigerons Way.
A police community support officer guarded the area and a mobile police unit was also set up nearby.
Police have appealed for anyone with information to contact officers at Rayleigh sexual offences investigation team on 101 or Crimestoppers anonymously on 0800 555111.