The incident happened at around 7PM in a house on West Street according to Lincolnshire Police.
The men have been taken to Pilgrim Hospital for treatment.
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Police were called to the house near The Oriental Palace Chinese Restaurant and The Eagle Pub.
The police said that there had been an altercation in the home. The stabbing didn't occur in public.
Three men have been arrested in connection with the incident. West Street had been closed off as a crime scene.
It follows a similar incident in June in which a man in his thirties was stabbed in a home on West Street.
Police are asking for those with any information on the incident to call 101.