There is "no sign" of life coming from President Ebrahim Raisi's helicopter, state TV says.
Reuters has also reported that the helicopter was "completely burned" in the crash, citing an Iranian official.
"President Raisi’s helicopter was completely burned in the crash... unfortunately, all passengers are feared dead," the official said.
Earlier, search teams have found the crash site of the helicopter carrying President Ebrahim Raisi, state TV says.
The head of Iran's Red Crescent Society has told state TV that the situation is not "good".
The cause of the helicopter crash is not yet known - but Iran has a poor air transport safety record.
This is at least partly the result of decades of US sanctions, which have severely weakened its aerial fleet.
President Raisi was on board a Bell 212 helicopter, state news agencies said. The model was made in the US and could not have been sold to Iran since the 1979 revolution.
Previous ministers of defence and transport, as well as commanders of Iran’s ground and air armed forces, have died in plane or helicopter crashes.
When reformers led Iran's government, they aimed to modernise the country's fleet of aircraft by negotiating a deal with the West that would see sanctions lifted in return for limiting Iran's sensitive nuclear activities and allowing in international inspectors
However, these efforts stalled when President Donald Trump withdrew from the deal and reimposed sanctions.
Reformers were subsequently opposed and mocked by hardliners, who insisted that Iran could rely on its domestic industries and foreign allies to improve aviation safety.
