Manuel Yerai, a farmer in southern Spain, watched helplessly on Monday night as hail the size of tennis balls ripped through the plastic sheeting covering his pepper plants, as Spain faced one of its most destructive rainfalls this year.

“My greenhouses look like they had been shot at,” Mr. Yerai, 40, said on Tuesday afternoon, speaking by phone from his farm in El Ejido, an agricultural region in Andalusia. Around him, he said, windows were shattered and cars were damaged. “The ground is full of sparrows,” he said, “dead on the sidewalks.”

Mr. Yerai is one of millions of people in southern and eastern Spain — including cities such as Valencia, Murcia and Malaga — hit by the immense deluge, which began in earnest on Monday night. In some areas, more than a month’s worth of rain fell in a day. In the region of Andalusia, it was four times the amount of rain that usually falls in all of October.

Spain’s meteorological agency said that between 150 and 200 liters per square meter, or roughly 40 to 50 gallons per square yard, fell in some areas over a two-hour period. And meteorologists expect the rains to continue until at least Thursday, if not through the weekend.

“These are huge amounts of rainfall,” said Rubén del Campo, a spokesman at the meteorological agency. He said that the amount of rainfall indicated “extreme danger,” and urged people to not travel unless it was strictly necessary.