London, Aug 10 : The UK is bracing for days of extreme temperatures in the latest heatwave, as the Met Office has issued a four-day amber warning for extreme heat in parts of England and Wales for Thursday to Sunday. According to the weather authorities, temperatures are set to climb to 35 degrees Celsius or even 36 degrees in some places, reports dpa news agency. The vulnerable are likely to experience adverse health effects and the wider population could also be affected, delays to travel are possible and there is an increased risk of water accidents and fires as more people head to tourist spots. The UK Health Security Agency has extended its level three heat health alert covering southern and central England from Tuesday until 11 p.m. on Sunday, with experts advising people to look out for those who are older or with existing health conditions, as well as young children. According to the Met Office, temperatures are not set to be as extreme as those in July which smashed records when the mercury climbed to above 40 degrees Celsius in some areas in the UK for the first time. The dry conditions, combined with last month's record-breaking heatwave, have depleted rivers, reservoirs and aquifers and dried up soils, hitting agriculture, water supplies and wildlife and raising the risk of wildfires. Meanwhile, there was no immediate sign of rain in the latest forecast from the Met Office. Temperatures are likely to rise into the low to mid-30s in the next few days in the area covered by the Met Office amber warning. Outside the warning area, heatwave thresholds, which are met at different temperatures in different parts of the country, are still likely to be met for much of the UK, with temperatures widely into the high 20s and a chance of a few spots seeing temperatures into the low 30s. Scotland and Northern Ireland will also see temperatures into the high 20s and could reach official heatwave criteria by Friday. The Met Office's fire severity index, an assessment of how severe a fire could become if one were to start, is very high for most of England and Wales, and will reach "exceptional" for a swathe of England by the weekend. /IANS