"This was an incredibly nasty incident and the staff were very shaken but fortunately unharmed, which is our number one priority.
"We will be offering them any assistance and any support they require after this terrible incident.
"We are also working with the police and hopefully witnesses will come forward to help catch these people."
More top news
Essex Police say they still want to find out what happened to Stuart Lubbock who died at Michael Barrymore's home near Harlow in 2001.
A High Court judge ruled he was entitled to "more than nominal" damages from police over a wrongful arrest he says destroyed his career.
The Anglia region has suffered its coldest start to August for many years and the summer weather is still on the showery side.