A man was taken to hospital after he suffered burns to his face and chest in a suspected "acid attack" in Chorley, say police.
Emergency services were called to a house on Mavis Drive in Coppull just before 10.30pm on Tuesday, April 10 after attackers sprayed a "corrosive substance" on the man.
Police say offenders knocked on the front door of the property, and smashed a panel spraying the man with the substance before he had a chance to open the door.
The man suffered burns to his face, chest, back and arm and was given first aid by firefighters who were tasked with making the scene safe.
Crime scene investigators and fire fighters remained at the house for most of Wednesday as they attempted to establish the exact nature of the liquid that was used.
Officers in the area are now reassuring members of the public by increasing patrols and are stressing that they believe this is a one-off incident.
A spokesman for the police said: "Unknown offenders banged on the door of the address, but before the occupiers had time to answer, they smashed the glass panel, reached in and sprayed what is believed to be a corrosive substance, before running off.
"Officers, paramedics and the Lancashire Fire and Rescue Service attended and a man who had suffered burn injuries to his face, arm, chest and back was taken to hospital where he is receiving treatment.
"We are treating this as an isolated incident at this time and patrols have been increased in the area."
Residents in the area spoke of their shock at the attack which happened in what they described as a "family" orientated street.
One resident, who did not wish to be named, said: "I have lived in this street for 40 years and I have several relatives who live here.
"We've never had anything like this happen around here before - people don't even break into cars.
"Lots of people were woken up by what happened and they were told to keep their windows and doors shut.
"It's just shocking - everyone looks out for each other here. A lot of the older residents are very worried.
"Nobody knows who lives in the house, they've only been there about a year."
Tony Whittaker, who lives in the area said: "My brother has lived on this road for 30 years. He's never had any trouble and it's a very quiet road. It's very unusual."
A spokesman for the ambulance service confirmed that a person was taken from a private address to a specialist burns unit at Whiston Hospital in Merseyside.
The severity of the man's injuries are unknown at this time.
A leading charity has condemned the attack and said that impact on victims can be devastating.
Alex Mayes, spokesperson for independent charity Victim Support said:“Chemical attacks can have a devastating and often long-term impact on victims, not only physically but also psychologically.
“Victim Support provides specialist practical and emotional support to victims of all crimes, including chemical attacks, whether or not the incident has been reported to the police."
Figures released by Acid Survivors Trust International reveal that the UK has one of the highest rates of recorded acid attacks in the world per capita.
The majority of the attacks are reported in London where in 2016 alone, corrosive substances were used in 454 crimes.