Days after an acid attack in downtown Hong Kong, and in preparation for a non-conventional attack on Israel, the National Emergency Authority (NEA) will hold the largest-ever exercise to train security forces how to respond to a citywide biological attack.

The drill will begin Wednesday with the arrival at hospitals throughout the center of the country of dozens of people with a variety of symptoms. The hospitals - including Ichilov, Tel Hashomer and Wolfson - will not know who the impersonators are and will have to work to identify them as well as the cause of their symptoms.

The scenario is a biological terror attack. The IDF Home Front Command will work to clear the infected area together with the Israel Police and Magen David Adom.

Defense officials said Tuesday that Israel needs to be prepared for a biological attack.

"We need to be ready for everything that can happen," said one senior official, who is involved in planning the drill. "There are crazy people running around the world who, with the right materials and access to the Internet, can carry out such an attack."

The official did not rule out the possibility that someone in Israel would copy the acid attack in Hong Kong on Saturday when bottles of acid were thrown from a building, injuring dozens of bystanders.

"This is terrorism," the official said. "There have been cases like this in the world and we need to make sure that the Israeli system works well and knows how to deal with such attacks."

One example, the official said, was an anthrax attack which was not contagious and takes several days for symptoms to appear. The symptoms, the official said, included high fever and overall fatigue, very similar to the flu.

"The trick is for the hospitals to be able to distinguish between the regular seasonal illnesses and the people who are suffering from abiological attack which requires special treatment," he said.