* Toyota plans to halt production at 12 Japan plants
* Over 150 flights cancelled, 18,500 households without power
* Search for people missing after volcano erruption suspended (Adds Toyota, Formula One race, updates storm impact data)
TOKYO, Oct 5 (Reuters) - A powerful typhoon was on course to hit the Tokyo area on Monday, after barrelling into southwestern Japan with heavy rain and wind that caused flights to be cancelled and knocked out power.
Typhoon Phanfone, which was downgraded from an earlier status of a super typhoon, is moving northeast at 25 kph (16 mph), after lashing parts of the Kyushu and Okinawa islands, the Japan Meteorological Agency said on Sunday.
About 30 cm (12 inches) of rain and heavy wind are forecast for eastern Japan, including the Tokyo metropolitan area.
"My school has already decided not to have classes tomorrow," said Tomoko Kakinuma, a 20-year old college student in Tokyo.
Toyota Motor Corp plans to halt production on Monday morning at 12 plants in Japan due to the storm, a company spokesman said.
On Sunday, several airlines, including All Nippon Airways and Japan Airlines Co, cancelled over 150 flights to several southern Japanese cities, broadcaster NHK said.
Kyushu Electric Power Co said about 18,500 households were without power late Sunday afternoon.
Nansei Sekiyu, a Japanese refiner wholly owned by Brazil's Petrobras, has suspended marine operations at its 100,000 barrels-per-day refinery in Okinawa due to the typhoon, but other operations are unaffected, a company spokesman said.
The approaching storm also forced the suspension of search efforts on Mount Ontake in central Japan, where 12 people remain missing following a volcanic eruption that killed at least 51, Kyodo news agency said.
Heavy rain delayed the Japanese Formula One Grand Prix on Sunday, which eventually saw two starts behind the safety car and ended before the full distance due to a crash. Britain's Lewis Hamilton won the race. (Reporting by James Topham and Chris Meyers; Editing by Kim Coghill)