The head was discovered at the quarry in Mepal, near Ely, Cambridgeshire, by a worker on Monday afternoon.
Police today confirmed that the head is damaged making it hard to determine if the remains are male or female.
Authorities say they are treating the death as "suspicious".
Police are also searching a site in Sharnbrook in Bedfordshire, from where the head may have been transported 40 miles to Mepal.
Specialist forensic teams have been searching using a JCB below Sharnbrook's historic viaduct.
A rail project is currently taking place on the land at Sharnbrook conducted by infrastructure specialists, Murphy, who have not commented on the events.
A spokeswoman for Cambridgeshire Police said: “We were called at about 3pm yesterday afternoon to reports of the discovery of a human head at a quarry in Mepal.
“Officers from the Bedfordshire, Cambridgeshire and Hertfordshire Major Crime Unit are conducting enquiries, both locally and across the county borders.”
A quarry worker, who would not be named, claimed his colleague made the discovery and thought it may belong to a woman in her 30s or 40s.
He said: "My colleague collected the skip where he saw nothing out of the ordinary, and put a cover over the top to stop anything falling out during transit.
"When he got back to our site, he took the cover off and spotted something straight away.
"He said, 'what on earth is that', and his first thought was that it was a manikin's head.
"But then he realised it had eyebrows and hair, and suddenly clicked that it was actually a woman's head.
"He said it had blood all over and was covered in dirt, but didn't look like it had disintegrated.
"He described the features of the head looking female and said she looked in her 30s or 40s, but he couldn't be 100 per cent.
"He thought she had dark hair but it could have been dirty blond and just covered in so much muck.
"He called the managers and it was all passed over to the powers that be."
A couple who live next to the site at Sharnbrook, Beds., where it is believed the head came from, always see lorries coming in and out of the area.
The couple, who have lived next to the site for 17 years and wished not to be named, said: "There's been forensics and I've seen someone walking with a couple of black bags.
"It's a big concern. I feel very sorry for those men.
"These men are doing nothing because they can't build anymore.
"There is always a night watchman in there so it couldn't have been someone trying to get in there at night who's then been found."
A spokesperson from Mick George Ltd, who owns the landfill site at Mepal, said: “We are working closely with the police and providing them with all the information they need to undertake their investigations.
“At this point we can not provide any further comments.”
No other body parts have been found by the police and they have launched a public appeal for information.
