According to the National Centre for Hydro-Meteorological Forecasting, the cold air mass reached mountainous and midland areas of northeastern Vietnam on the evening of October 4.
At about 6 am on October 5, temperatures in Hanoi stood at around 22 degrees Celsius. Light rain in some areas made the change in weather more noticeable for people heading out early.
Long Bien Bridge was shrouded in light morning rain, with cyclists and motorcyclists wearing raincoats to keep dry and warm.
Under the bridge, traders carried on with their usual business. Vendors began preparing their goods early, adding raincoats or long-sleeved clothing to keep out the chill and drizzle.
In the Hoan Kiem Lake area, many residents kept up their routine of exercising, walking and jogging from early morning.
Many older people put on warmer clothing as the weather changed abruptly and temperatures fell sharply compared with previous days.
Across many streets in the capital, warm jackets began to appear among the morning commuter crowds.
Schoolchildren also arrived in winter uniforms, signalling that the colder season was gradually making itself felt in the capital.
Along West Lake, gusts sweeping across the water carried a chill that made the cool, crisp feel of the early-season weather easy to notice.
After their morning exercise, many people lingered over cups of hot tea, chatting while enjoying the cool air. For many, this is one of the clearest signs that Hanoi has entered the first days of the cold season.
People could easily feel the season's first chill when passing through areas lined with tall buildings and wide open gaps that funnelled strong winds.