The cause of a West Auckland house fire that critically injured a man has been determined by investigators, but police are still investigating whether it's suspicious.

The man was rushed to Auckland City Hospital on Thursday afternoon after a blaze took hold of a Kelston home about 2pm.

The man was in a critical condition and on Friday he was transferred to the burns unit at Middlemore Hospital.

Fire investigator Chris Lewis said the cause of the fire had been determined and the matter handed to police.

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He declined to comment further.

A police spokeswoman would only say that inquiries into the blaze were continuing to determine if there were suspicious circumstances.

A Counties Manukau District Health Board spokeswoman couldn't confirm the man's condition on Friday afternoon, because he hadn't officially been registered as a patient yet.