Italian, Swiss and Austrian authorities on Wednesday halted the sale of flu vaccines made by Swiss pharmaceutical giant Novartis.

The Italian health ministry said it has banned the sale and use of several flu vaccines produced by Novartis pending tests into possible side-effects.

"The health ministry and the Italian medicines agency (AIFA) have decided to take the precaution of banning immediately the use of the vaccines" Aggripal, Fluad and Influpozzi, it said.

On the basis of information supplied by Novartis, AIFA "has decided that it is necessary to carry out further tests regarding the quality and the safety" of the vaccines, which "can produce collateral effects," the statement said.

In Switzerland, the national drug agency Swissmedic said it was ordering the "immediate halt of flu vaccine deliveries from Novartis," due to "possible impurities".

The alarm was raised after white particles were seen in syringes carrying the vaccines, Swissmedic said, stressing that they could be nothing more than little clumps of the vaccine's components.

The Swiss decision affects some 160,000 vaccine doses, Swissmedic said, adding that it was unclear whether the problem affected vaccines already available in Switzerland.

The freeze on sales of the vaccines and their use was "a simple precaution" and those who had already been vaccinated for the flu "had nothing to worry about", it added.

In Austria, a spokeswoman for Novartis's Austrian subsidiary said that "further deliveries of the Novartis flu vaccines were stopped today (Wednesday)."

She added that the move was a precautionary measure following the moves by Italy and Switzerland.

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In their statement explaining the freeze on vaccine imports, Italian authorities said they had "decided that it is necessary to carry out further tests regarding the quality and the safety" of the vaccines.

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In Austria, a spokeswoman for Novartis's Austrian subsidiary said that "further deliveries of the Novartis flu vaccines were stopped today (Wednesday)."

She added that the move was a precautionary measure following similar decisions by Italy and Switzerland.