About 10 people have come forward with health concerns and 229 people have been evacuated from their offices since Tauranga City Council confirmed about 30 per cent of its building had tested positive for toxic black mould.

Almost half of the council's 520 staff have been relocated. The first floor and part of the ground floor has been sealed off to stop the mould's spread.

Staff in white paper boiler suits and masks could be seen wheeling computers out of the contaminated areas which had been sealed off with thick black plastic and masking tape.

Tauranga City Council chief executive Garry Poole said the first tests to come back on December 4 revealed "abundant levels of stachybotrys which is commonly known as black toxic mould". On Thursday results came back confirming the mould was more widespread.

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Since the announcement toxic black mould had been found about 10 staff had come forward with health concerns and had been referred to their GP at the council's cost, Mr Poole said.

They reported asthma-like symptoms and skin irritation.

The results of further tests on other parts of the building, including the four city libraries, the i-Site and the council chambers, were due back by Friday but would remain open in the meantime. Mr Poole said he was confident there was no risk to staff or customers.

When staff arrived at work yesterday they were told how they would be affected, Mr Poole said. Yesterday 146 staff had been relocated within the building or in other central city buildings, 59 were working from home and 24 were given paid leave until a workspace could be found.

All staff would be fully operational by midday today but 59 people would continue working from home.

Emergency recovery specialist Terry Wynyard, who was appointed project director to manage the issue, said they have started to clean the building and decontaminate equipment.

Mr Wynyard said experts had advised vacuuming the chairs floor and wiping down hard surfaces with hot, soapy water and drying them with paper towels would make them safe.

Some walls may have to be removed to get rid of the mould.

"The mould can live in GIB board, any surface where there's a fibre, but it has to have moisture content to allow it to survive," he said.

"When it's wet it tends not to move because it's kind of glued to the spot. The issue with the mould is when it dries it can become airborne ... and that is the situation there. One of the issues we're managing is dry mould moving through the air and people moving it around."

The air conditioning system had been found to be successfully filtering the air and stopping the spread of the substance.