Another man was in custody after the incident in Skelmersdale.
A Lancashire police spokesman said: “Shortly before 6am today (Thursday) we were called to an address on Tanfields, Skelmersdale.
“On arrival officers found a man had suffered stab wounds to both legs.
“He was taken to Aintree Hospital, where he remains in a critical condition.
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“A 37-year-old man from Skelmersdale has since been arrested on suspicion of assault – GBH, and he remains in police custody.
“Our enquiries are ongoing.”