The families had walked up the mountains to see the unseasonal weather conditions for themselves but then got stuck as darkness fell because of the severe cold and exhaustion. One of the families had a baby in a pram.
Hundreds of people had made their way to the summit of the island, more known for its wall-to-wall sunshine, following two days of snowfall.
The authorities had to close off roads and warn local residents and tourists to keep away because of the extreme conditions.
Police said many ignored the alert and got out of their cars to continue on foot, even jumping over barriers and fences.
The island’s government confirmed on its Twitter site that the emergency services had to be called in last night to rescue the stranded group of 40, many of whom were on the brink of suffering hypothermia.
“More than 40 people have had to be evacuated, including adults with children and a baby in a car, the elderly and people with health problems. One had to be transported in an ambulance,” said a spokesman.
Even at 1pm in the afternoon, a temperature of 3.5 degrees was recorded, with heavy snowfall. The conditions then continued to deteriorate and it became even colder, with some of the sightseers still trying to walk down the mountain at 9pm.
The emergency services took the stranded 40 to a rural hotel below the summit to recover.
Snow also hit other high points of the Canary Islands including on Mount Teide in Tenerife where an access road also had to be closed for some time.