Welles’s Mercury Theatre on the Air normally reached only a small portion of the radio audience. Much more popular was The Chase and Sanborn Hour, a variety show. But Chase and Sanborn listeners would often change channels after hearing a popular act like the ventriloquist Edgar Bergen. An estimated 4 million of them switched to the CBS network to find The War of the Worlds already playing, thereby missing Welles’s initial announcement that it was a drama. An estimated 6 million Americans listened to some portion of the broadcast, and nearly a third of them took the play as fact.
The nation was on already on edge. Five weeks earlier, the worst hurricane of the century had killed 600 people along the eastern seaboard. During September, radio correspondents had frequently interrupted programs with bulletins about the Munich crisis in Europe. War was in the air.
After landing in Grovers Mill, New Jersey, the Martians started fires, brushed aside militia units, and marched toward New York City spreading poison gas. As the play continued, phone lines clogged with listeners calling radio stations, police headquarters, and relatives. Those who couldn’t get through saw the congestion as further evidence of disaster. Many listeners, surrendering to the power of suggestion, actually saw the flash of bombs and smelled the gas.
Here's the New York Times coverage on Oct. 31, 1938.
The broadcast, which disrupted households, interrupted religious services, created traffic jams and clogged communications systems, was made by Orson Welles, who as the radio character, "The Shadow," used to give "the creeps" to countless child listeners. This time at least a score of adults required medical treatment for shock and hysteria.
In Newark, in a single block at Heddon Terrace and Hawthorne Avenue, more than twenty families rushed out of their houses with wet handkerchiefs and towels over their faces to flee from what they believed was to be a gas raid. Some began moving household furniture.
Throughout New York families left their homes, some to flee to near-by parks. Thousands of persons called the police, newspapers and radio stations here and in other cities of the United States and Canada seeking advice on protective measures against the raids.