The Ping River is slightly subsiding, but the situation in Chiang Mai city remains critical as floodwaters have caused damage to economic areas.
The water level at Naowarat Bridge in the municipality was 4.80 metres deep at 10am on Thursday, down from 4.93m at 2am, which broke the previous record of 4.90m set 13 years ago.
The municipality warned that the crisis was not over. "The Ping is red-flagged and is in crisis," it added.
The overflow of the river has wreaked havoc in downtown Chiang Mai, including the famous Night Bazaar, with water levels in some locations reaching as deep as one metre.
The Regional 1 Health Centre in Muang district, better known by its former name as Chiang Mai Mother and Child Hospital, closed on Thursday due to flooding. Lanna 3 Hospital announced that it will not accept patients except for emergencies until Monday, as floodwaters have entered the first floor of its buildings, including emergency wards.
Kuakul Manasamphansakul, the provincial irrigation chief, said floodwaters were moving towards Chiang Mai railway station and towards Highway 11, known as the Super Highway, which is the main road linking the city with Lampang.
The official said that residents on the other side of the road would be safe, as floodwaters will not flow across.
Authorities have advised people living near the railway station to move belongings and vehicles to safe locations since Wednesday. Officials are closely monitoring the large volume of water being released from the Mae Ngad Somboon Chon dam in Mae Taeng district, which is expected to reach the municipality 20 hours later.
Mr Kuakul said authorities will try to manage the water flowing downstream from the dam to the city. He warned people in Lamphun to prepare for flooding within days.
"The water level of the Ping will increase, but it will not reach the highest point of 4.93m," the irrigation chief said.
Prime Minister Paetongtarn Shinawatra has instructed officials to swiftly drain floodwater out of economic areas in Chiang Mai. She plans to visit flood-hit Chiang Rai and possibly Chiang Mai as early as Friday.
The State Railway of Thailand (SRT) announced that train services between Chiang Mai and Lampang are still halted due to flooding. All trains are currently stopped at Lampang station, and all passengers travelling to and from Chiang Mai are being transported by bus.