A construction worker found the remains on Wednesday during a routine excavation near a power cable in a manhole located at Ground Zero, the site of the collapsed World Trade Center, said a spokesman for the Port Authority of New York and New Jersey, which owns the site.
Workers from utility company Consolidated Edison (Con Ed) found more human remains on Thursday, said the spokesman, Steve Coleman.
"The remains were found following the removal of materials from manholes that had been inaccessible since 9-11," Con Ed said in a statement.
The company said it was assisting police and the medical examiner's office in connection with the discovery.
"We share the great sensitivity felt by families and rescuers associated with the tragedy, since many of our employees have been personally involved in the restoration and recovery efforts," Con Ed said.
The latest discovery this week has further angered families of victims.
The WTC Families for a Proper Burial expressed its "outrage at the continued cavalier attitude toward the retrieval of human remains."
The group called on authorities "to complete a thorough search for all human remains, keeping in mind that there are still 1,151 victims for whom there are absolutely no remains."
Such discoveries are not new. Six months ago, bone fragments were found on the roof of the condemned Deutsche Bank skyscraper, which was damaged in the attacks.
The double suicide plane attack on the twin towers left 2,749 people dead.
Nearly 3,000 people died when hijackers crashed planes on the World Trade Center, the Pentagon and a Pennsylvania field.

Copyright AFP (Agence France-Presse), 2006