Police uncover possible clue in the search for William Tyrrell

Police have found a piece of fabric while draining a creek in the search for William Tyrrell's remains on the NSW Mid North Coast.

An eight-by-eight centimetre piece of faded blue fabric was found near the creek in Kendall.

The fabric was marked, photographed and bagged for forensic testing.

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It comes after officers spent more than three hours draining a creek, as investigators searched beyond the initial area they had been looking in.

Officers also searched soil in the same pocket of bushland, running small sections through a motorised sieve.

The extensive search has brought in several experts including an archaeologist, forensic anthropologist and a water expert.

Meanwhile more than a dozen officers today worked on the first area identified in the search, with no significant breakthroughs so far.

Several pieces of string have so far been found, with testing ongoing.

Australian Federal Police used ground-penetrating sonar over a concrete slab at the nearby home William disappeared from, but detected no anomalies.

The results of luminol testing to detect blood beneath the home's balcony are also underway, as detectives investigate the possibility that William fell from the balcony and was then transported into the bush.

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William was three when he disappeared from the Kendall home on September 12, 2014 and he has never been found.

The new searches were launched this week, with police confirming they were looking for William's remains.

Today marks the fifth day of the search for William's remains.

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A car that formerly belonged to William's now-deceased foster grandmother was also seized and is undergoing forensic testing.

William's foster mother is being treated as a person of interest in the case.

She has not been arrested or charged.