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.
A dry creek overflowed, creating a strong current of water and mud that buried cars and tore trees along the way, witnesses told Spain's TVE.
Local radio reported the death of the pair, along with at least three others, as torrential rainstorms hit the town of Sant Lorrenc - 40 miles east of the capital of Palma - on Tuesday night.
The UK Foreign Office is supporting families of two British people who are among those to have died.
Antonia Bauza, deputy mayor of Sant Llorenc des Cardassar, the worst-hit town, confirmed that two of the victims were British citizens.
At least 10 people have died in the floods. "We had to swim to try to survive".
The regional government called an emergency meeting, and authorities said 630 rescue workers and military units had been sent to the area to help.
The couple, who were in their 70s, are said to have died along with cab driver Juan Sillero when the vehicle was swept away by a torrent of water near the coastal resort of S'Illot. The flooding also affected phone communications, destroyed two bridges and forced the closure of 11 roads.
Dramatic video footage on social media shows raging torrents of water gushing through the streets of the town, with reports that more than 20 centimetres of rain fell in just four hours.
The weather agency, AEMET, said more heavy rainfall is expected Wednesday in eastern and southern parts of the Iberian peninsula.
He was planning to travel to the area later on Wednesday, his office said.
Lawmakers held a minute's silence before the weekly prime minister's question time in parliament on Wednesday morning.
Heavy rain has also brought flooding to other parts of Spain, including Barcelona and the Costa del Sol.