An aircraft with 21 people on board has crashed in a mountainous region of northern Nepal, police said on Monday.

"There were 18 passengers and three crew members. It's a remote area so there is no telephone network but we fear there may be many deaths," police spokesman Binod Singh told AFP.

Singh said the Agni Air plane crashed into a hill near Jomsom, a popular area for trekkers near the Annapurna mountain range.