A police investigation has been launched after a toxic substance was posted through a letterbox.

The incident, which happened between 10pm on Wednesday and 8am on Thursday morning on Cowper Avenue in Tilbury, has left two people needing hospital treatment.

A spokesman for the East of England Ambulance Service Trust said: “We received a called to support our emergency services colleagues at 9.20am.

“Three rapid response vehicles, one ambulance and the hazardous area response team attend an incident in Cowper Avenue, Tilbury.

“This was believed to be a chemical-related incident.The response was led by the fire service.

“One man and one woman, both conscious and breathing, were treated at the scene and taken to Basildon and Thurrock Hospital for further treatment.”

Essex Police are investigating the matter and are looking for information from potential witnesses.

A small black glass display table was stolen and an unknown substance was poured on the floor and through the letterbox, which was later identified as a cleaning agent by Essex County Fire and Rescue Service.

DC Mark Miller said: “We are keen to find whoever is responsible for this crime.

“The use of the cleaning agent ensures that there is little physical evidence, so any eyewitnesses are crucial.”

Also in attendance at the scene on Thursday morning were the fire service. Although they initially did not know what the substance was, they later determined that it was cleaning agent.

A spokesman for Essex Fire and Rescue said: “The immediate area around the property has been temporarily cordoned off as a precaution. Tests are being carried out by officers to identify what the substance is.

“This is a localised incident, and there is no wider concerns for the public.

“We have identified the substance as a cleaning agent – there is no risk to the property, occupants or wider public.

Anyone who saw anything suspicious is asked to call 101 and ask for Grays CID.

Alternatively, you can contact the Crimestoppers charity 100 per cent anonymously on 0800 555 111 or use the anonymous online form at Crimestoppers-uk.org.