The Aurora Borealis or Northern Lights illuminate the night sky over Chena River State Recreation Area near Fairbanks, Alaska, the United States, on Oct. 5, 2016. (Xinhua/Li Changxiang)

SAN FRANCISCO, July 5 (Xinhua) -- Anchorage, the largest city in the U.S. state of Alaska, Thursday broke the all-time high temperature in 50 years when it hit 90 degrees Fahrenheit (32.2 degrees Celsius), the National Weather Service Anchorage (NWS Anchorage) said in an evening report.

The hottest temperature on July 4, Independence Day, was registered for the first time at the Anchorage International Airport at about 5:00 p.m. local time Thursday (0100 GMT Friday), which officially broke the 50-year record, said NWS Anchorage.

The weather service of the municipality of Anchorage tweeted that the previous record in the area was 85 degrees Fahrenheit (29.4 degrees Celsius), which was set on June 14, 1969.

The exceptionally warm temperatures are caused by a "giant ridge of high pressure sitting right over us," said NWS Anchorage meteorologist Bill Ludwig, quoted by the Anchorage Daily News.

The weather forecast said the next three days will experience above-normal temperatures in the city, ranging between 81 degrees Fahrenheit (27.2 degrees Celsius) and 84 degrees Fahrenheit (about 28.9 degrees Celsius).

The normal high temperature for July 4 in Anchorage is 65 degrees Fahrenheit (18.3 degrees Celsius), said the newspaper.

The exceptional heat spell, combined with dry conditions, has caused worries about wildfires in Anchorage and other cities.

More than 30 large fires have been reported in Alaska, including the Swan Lake fire burning on the Kenai Peninsula southwest of Anchorage, according to the weather.com website.