As the search to locate President Raisi continues, Iranians have gathered for vigils on the streets of the capital, Tehran.
Bad weather - with heavy fog and rain - is hampering the efforts of rescue teams to get to the accident site in the mountains in the northwest of Iran.
The condition of those on board the helicopter remains unknown for now, with reports that no contact has yet been made.
President Raisi was travelling with the Iranian foreign minister in a convoy of three helicopters over the area - two of the helicopters are reported to have landed safely.
Raisi was elected president on his second attempt in 2021.
He is seen as a hardliner and regarded as a potential successor one day to Ayatollah Khamenei as Supreme Leader.
