Residents of Gorkha began reporting flooding in the Budhigandaki river on social media before 5am on Sunday, but the National Disaster Risk Reduction and Management Authority (NDRRMA), in a report released on Monday, said a landslide had blocked the river at 5:30am.

Suna Gurung, a driver staying at a hotel in Jagat Bagar in Sirdibas, posted a warning on Facebook at 4:59am on Sunday.

“Everyone downstream, stay alert. The Budhigandaki is flooding,” he wrote.

Gurung had received an earlier warning from an acquaintance, who called him at 4:45am from Ghattekhola, above Sirdibas.

“A landslide has blocked the river, and a flood like the one in the Bhotekoshi river has arrived. Run quickly,” the caller told him.

However, the NDRRMA’s Gorkha-Budhigandaki Flash Flood: Search, Rescue and Relief Response Report, released on Monday, states that a major landslide occurred at 5:30am on Shringi Himal, between Lokpa and Chumling in Chumnubri Rural Municipality-6. The landslide blocked the Wingilung stream, and the Budhigandaki river was subsequently blocked as well, triggering a massive flash flood carrying mud and debris, the report says.

After receiving reports of sudden flooding in the Budhigandaki river, eight Nepal Police personnel helped evacuate residents and 12 employees of Times Energy Pvt Ltd, based in Salleri, to safer locations, the authority said.

Five people from Wingilung and Chumchet in Chumnubri-6 remain unaccounted for.

The Nepali Army deployed four helicopters to rescue people from affected areas, bringing 95 people, including nine foreign nationals, to safety.

SMS alerts at 6am

After receiving information about the flooding, the NDRRMA sent SMS messages urging 221 emergency responders in Gorkha, Dhading, Tanahun, Chitwan, Nawalparasi East and Nawalparasi West to mobilise immediately. The Nepali Army also conducted an aerial inspection of the affected areas, the authority said.

According to the report, water began flowing through the blockage at 6:15am, triggering a major flood. Residents living along the riverbanks were subsequently moved to safer locations.

What the NDRRMA report says

· 6:30am: Water levels at the Budhigandaki-Arughat gauging station rose from 2.28 metres to 3.66 metres. With the warning threshold at 4.50 metres, SMS alerts were sent to residents along the riverbanks. The report says around 200,000 warning messages were sent.

· From 6:30am: Response meetings and coordination efforts began under the chairmanship of NDRRMA Chief Executive Dharam Raj Uprety, with Home Minister Sudan Gurung in attendance.

· 6:36am: The Nepali Army began search and rescue operations by helicopter, taking six people to safety.

· 7:50am: Water levels at the Arughat gauging station reached 5.01 metres, exceeding the danger level of five metres.

· 8:30am: The river level at the gauging station rose further to 6.22 metres. A total of 437 security personnel from the Nepali Army, Nepal Police and Armed Police Force were deployed in the affected areas. Another 50 Nepal Police personnel were kept on standby.

· 8:40am: Water levels at the Arughat gauging station climbed to 8.43 metres.

· 10am: Essential relief supplies began being transported to the affected areas by road and helicopter.

· 11am: The Nepali Army deployed four helicopters to the affected areas. By that time, 95 people had been rescued and taken to safety, according to the report.

· From 11am: The federal Ministry of Health and Food Safety and Gandaki Province’s Ministry of Health placed district rapid response teams in Gorkha, Lamjung and Tanahun, along with emergency medical teams from provincial hospitals, on standby.

· 1pm: Teams were deployed to assess road access and investigate the cause of the flooding. A team including the directors-general of the Department of Roads and the Department of Local Infrastructure Development was sent to assess access routes and examine the possibility of installing a Bailey bridge. Separately, the NDRRMA deployed a three-member team comprising a drone operator and a geologist to investigate the cause of the disaster.

· 2pm: The number of security personnel deployed in the affected areas reached 703, comprising 171 Nepali Army personnel, 143 Nepal Police personnel and 389 Armed Police Force personnel. Response teams then updated damage assessments and discussed the next steps for rescue and relief operations.