A 15-month year old Greymouth boy at the centre of a police investigation has been named.

Leith Hutchison died on Tuesday last week after he was taken to Grey Base hospital in cardiac arrest.

Medical staff later found the boy was suffering from a bleed on his brain.

Detective Senior Sergeant Dan Keno says police aren't ruling anything out, including the possibility that some form of assault may have taken place.

"This is a tragic loss of such a young life and my deepest sympathies go out to all of his family."

Investigators are speaking to family members and anyone who had been in contact with the boy in the last few weeks of his life.