POLICE are investigating how a hoax package containing a harmless white powder came to spark a chemical attack alert at a York city centre bank.

A massive emergency services operation was mounted after staff at NatWest Bank in Market Street returned from the Bank Holiday break to discover the suspicious substance inside an envelope, just before 9am yesterday.

Shops were closed and parts of Market Street and Coney Street sealed off until 3pm as chemical, biological, radiological and nuclear advisers from the fire, ambulance and police services worked to determine what the substance was.

Police said they were treating the discovery as a "worst case scenario" although workers at nearby H Samuel Jewellers in Market Street were told by officers the incident was "nothing to worry about".

Crowds of onlookers gathered behind police tape and shop staff watched from windows as two temporary decontamination showers were erected outside Woolworths.

A team of firefighters and paramedics in decontamination suits went inside the building to remove the parcel, which had been placed in an isolated room at the bank.

They also brought out two staff who had handled the substance and put them through a decontamination procedure as a precaution, before taking them to hospital.

Other NatWest workers remained sealed in the building.

Forensic tests later showed the substance was harmless and the area was reopened.

Inspector Alex Brandom, of York Police, told the Evening Press officers were trying to establish who was behind the hoax.

"We are investigating a potential crime scene and we will be conducting further forensic examinations," he said.

"Further inquiries are now being made to try and establish who, why and how the items came to be at NatWest."

NatWest remained closed for the rest of the day following the incident, as did the neighbouring Scarborough Building Society.

A NatWest spokesman said the bank had "no comment" because the matter was being handled by police.

Updated: 10:21 Wednesday, March 30, 2005