Nepal has observed a national day of mourning for victims of devastating floods that have killed at least 1,398 people, as rescue teams continue searching for thousands of missing people.

The disaster began on August 26 after a glacial and mountain collapse near the Nepal-China border triggered massive floods and mudslides across affected areas.

More than 5,500 people remain missing, including about 800 foreigners, according to reports.

Monday marked the 13th day since the disaster, with government offices lowering national flags to half-mast as families carried out mourning rituals for relatives who died or remain unaccounted for.

Some families have held symbolic funerals for missing relatives despite the absence of recovered bodies, following traditional Hindu mourning practices.

Rescue operations have increasingly focused on 12 hydropower projects where about 900 workers remain missing, with roughly 500 believed to be trapped inside tunnels.

Specialised teams from India, China, South Korea, the United States and other countries are supporting Nepalese rescuers as they search damaged facilities and tunnels for survivors.

The rescue effort received a boost after several people were found alive in recent days, including two Nepalese workers rescued from a hydropower tunnel and a Chinese national recovered from another facility.

Nepal's Ministry of Foreign Affairs said 13,396 people had been rescued as of Monday, while 1,355 bodies had been recovered and about 5,000 people remained missing.

Authorities said search and rescue operations would continue on the ground, in the air and inside tunnels, with international teams providing specialised equipment and technical support.

Families of missing hydropower workers have continued to press the government to intensify rescue efforts, as hopes remain for survivors trapped in underground spaces where air pockets may still exist.