Italy battled scorching temperatures on Thursday as the ministry of health issued a "red alert" in 18 cities across the peninsula.

The ministry's heat alerts go from level 0 (green, or no risks to human health) to level 3 (red), meaning a heat wave with "conditions of high risk persisting over three or more consecutive days."

The red alert was issued in popular tourist cities such as Florence, Milan, Rome, and Venice, where the heat wave is expected to last through Saturday with temperatures peaking at 38 degrees Celsius.

The ministry recommended staying indoors between 11 a.m. and 6 p.m., and avoiding parks during the hottest hours of the day due to excessive ozone levels.

A rise in ozone is "a public health problem especially for children, the elderly, asthma sufferers, and people with lung or heart disease," the ministry said.

Florence authorities have set up meal delivery and other support services for the elderly. Milan activated an emergency number where the elderly and the disabled can call for home assistance.

In Rome, local health authorities distributed water bottles to crowds of tourists thronging the Imperial Forums. They also increased the number of available beds in shelters for the homeless.

In Venice, social services set up air-conditioned centers for the elderly and other at-risk populations.

The Civil Protection Agency warned against the risk of wildfires caused by arsonists or human negligence. Fires have destroyed 12 percent of Italy's forests over the past 30 years.