Part of the historic wall in Chiang Mai has crumbled after heavy rain, as weather forecasters issued a storm watch across the country from Tuesday.

A section of the wall at Chang Phuak Gate at the moat collapsed on Sunday due to soil that absorbed too much rain.

The collapsed section was built in 1957 to replace the earlier outer part of the ancient wall that surrounds the central area of the city.

Rain has hit the northern province over the past few days - and in the weeks before - and the Meteorological Department expected more rain and thunderstorms in Chiang Mai throughout the week.

The weather agency has issued a storm alert for most parts of the country between Tuesday and Thursday as Super Typhoon Noru is expected to reach the Vietnamese coast during the period.

Its landfall in Vietnam would send rain, gusty winds and some downpours into provinces in the northern, northeastern, central and eastern regions, the Meteorological Department warned.