Two of the victims were British nationals, said Antonia Bauza, the deputy mayor of Sant Llorenc, the town hardest hit by the downpours, which is about 60 kilometers (40 miles) east of Mallorca's capital, Palma.
According to Spanish meteorological agency Aemet, more than 8in (20cm) of rainfall in just a few hours hit the island on Tuesday.
Two British nationals are among those among the confirmed dead.
Rivers burst their banks, and swamped homes - forcing some people to take shelter in a sports center in the nearby town of Manacor.
A destroyed auto and debris are seen on the street as heavy rain and flash floods hit Sant Llorenc de Cardassar on the island of Mallorca, Spain, October 10, 2018.
The British pair reportedly died in a taxi in the Sant Llorenc area of this island after strong torrents formed during intense showers.
A Foreign Office spokesman said: "We are supporting the family of two British people following their deaths in Spain, and will do all we can to assist them at this deeply hard time".
Video footage showed cars turned upside down, damaged houses and trees in the road.
The authorities said 80 soldiers from the military emergency unit would join more than 100 rescuers working in the area this morning after eight inches of rain fell in four hours on Tuesday evening.
The Spanish Prime Minister, Pedro Sanchez, added: "My solidarity and support goes out to the families and friends of victims and all those affected by these tragic floods".
A spokesperson for his office says he will visit the areas affected by flooding later on Wednesday.