Emergency services have been called to the High Street, Lee-on-Solent just before 10am.
Police and specialist fire crews have been called to a property following a man being attacked in the early hours of the morning.
Hampshire police say a 47-year-old man is in hospital following the assault and an investigation is underway.
It is believed that Police Officers were called just before 4.15am this morning to a report that a 47-year-old man had been assaulted on the High Street in Lee-on-the-Solent.
The man has been taken to hospital for treatment and enquiries are ongoing to establish the circumstances of what has happened.
A specialist DIM (Detection, Identification and Monitoring) vehicle from Hampshire Fire and Rescue service has been called in to analsye the unknown substance. A police cordon remains in place, and the public have been asked to avoid the area for the time being.
A Spokeswoman from Hampshire police say a 47-year-old man is in hospital following the assault and an investigation is underway.