Workers have recovered more human remains from several manholes as New York began a new search for September 11 victims.

The search was prompted by the surprise discovery of dozens of bones in an abandoned manhole this week.

Utility and city chiefs hand-removed material from other manholes after tearing into the pavement on a service road along the site’s western edge. It was then sifted on-site by forensic officials for fragments of human remains, said deputy mayor Edward Skyler. City chiefs said about 15 more pieces of remains had been recovered, bringing the total to nearly 100 this week.

Distraught relatives of some September 11 2001 victims called for a new government-led search for remains in and around ground zero after building workers discovered bones in one manhole excavated as part of work on a transport hub. The unexpected recovery prompted the city to order a more thorough search of underground cavities that may have been missed.

The 80 bones and fragments ranged from a little less than an inch to 12ins long, said Ellen Borakove, spokeswoman for the city medical examiner’s office.

The active search ended in 2002 after a massive clean-up of 1.5 million tons of debris. About 20,000 pieces of human remains were found, but the DNA in thousands of those pieces was too damaged by heat, humidity and time to yield matches in the many tests forensic scientists have tried over the years.

More than 40 per cent of the 2,749 September 11 victims in New York have never been identified.

Some relatives have asked for the city to enlist the help of a military unit known as the Joint POW/MIA Accounting Command, which specialises in finding and identifying the remains of missing troops. The mayor’s office said in a message to the families that two experts on the city’s forensic team were former members of that unit.