A relentless heat wave has baked Hainan province for days, with temperatures soaring above 40 C and experts expecting little relief until at least April 16.

Hainan's provincial meteorological bureau issued a Level 4 heat warning on Saturday, saying to anticipate highs between 37 and 39 C with localized 40 C readings. The temperature in Tunchang county set an April record at 40.4 C.

The warm temperatures arrived unusually early and cover nine cities and counties, with more than a dozen others under a heat alert. According to the Hainan Climate Center, the year's first 37 C day typically occurs in April in the western and northern parts of the island, and between May and July elsewhere. This year, Ding'an county hit that mark 42 days early, the second-earliest since 1991. Tunchang and Qiongzhong Li and Miao autonomous county also saw top-three early arrivals.

Li Yumei, chief forecaster at the meteorological observatory, said the scorching conditions stem from a southwesterly low-pressure trough that pulls hot, dry air from Indochina across the island's central Wuzhi Mountain range, creating a foehn effect that heats air by about 1 C per 100 meters of descent. Meanwhile, a strong, persistent subtropical high has kept skies clear and intensified surface heating.

The heat is worsening a deepening drought. By Monday, severe drought gripped Wenchang and Qionghai, with 11 other cities and counties experiencing moderate drought.

Agriculture is suffering. Early rice is in its critical heading and flowering stage and is susceptible to high temperatures. Farmers are advised to ration irrigation or spray water to cool crops. The heat also negatively affects fruit. Scientists recommend drip irrigation, crop residue mulching to cool soil and retain water, and nutrient sprays to protect against heat.

Daily life has also been disrupted. Fan Yu, manager at China Construction Third Engineering Bureau Group's Hainan Medical University project, said outdoor workers have shortened hours to avoid working from 11 am to 2:30 pm and are receiving free iced mung bean soup, herbal tea, and medicine. Health officials caution against heatstroke and other heat-related illnesses.

Authorities in Haikou and other areas have prepared for cloud-seeding, which will be carried out to help alleviate the drought once cloud conditions are ideal.

Forecasters expect the heat to expand across southern China in the coming week, with temperatures surpassing 35 C in many areas.