TOKYO -- Japan's major nuclear reactor manufacturers have begun developing small nuclear power systems for both developed and emerging countries, a report said on Saturday.

Toshiba Corp. is developing an ultra-compact reactor with an output of about 10,000 kilowatts and has started procedures for approval in the United States, the Nikkei business daily said.

The new reactor, the Toshiba 4S, is designed to minimize the need for monitoring and maintenance, with an automatic shutdown function to ensure safety in case of problems, the newspaper said.

Toshiba plans to market the reactor first in the United States, while foreseeing demand from emerging countries in Southeast Asia and Eastern Europe as well as in Africa, it said.

Mitsubishi Heavy Industries Ltd. has separately completed the concept design for a pressurized-water reactor with a power output of around 350,000 kilowatts, the Nikkei said.

Hitachi Ltd. also aims to develop a boiling-water reactor with a capacity of 400,000-600,000 kilowatts for use in Southeast Asia and other countries, it said.

Demand for nuclear power stations has been growing around the world. A total of 151 were under construction or slated for construction in 27 countries as of the end of 2008, it said.