JAPAN'S All Nippon Airways, the single biggest operator of Boeing's flagship 787, said it put its Dreamliner fleet back into service yesterday following a four-month suspension due to battery problems.

ANA said one of the high-tech planes departed "safely" yesterday afternoon from Sapporo in Hokkaido to Haneda in Tokyo as a relief service with some 220 passengers aboard.

It was ANA's first commercial flight of Dreamliners since the planes were grounded worldwide after two separate incidents on Japanese-owned planes involving overheating of the lithium-ion battery packs in January.

"We have implemented full-scale preparations with some 200 test flights," ANA Vice President Hiroyuki Ito was quoted by Jiji Press as saying in Sapporo's Shin-Chitose airport ahead of the departure.

"We will continue to make our efforts so that people can use the flights comfortably," Ito said.

A passenger on the flight told Tokyo Broadcasting System Television at the airport: "To be honest, I feel a sense of unease but I want to believe in ANA."

Last week ANA announced plans to resume the flights earlier than its originally planned date of June 1 as the airline completed safety tests.

ANA plans to restart regular flights at home and overseas, including services connecting Tokyo and major cities such as Beijing, Frankfurt, San Jose and Taipei.

After months of investigations, US authorities in April formally approved Boeing's battery fix and Japanese regulators followed suit.

In mid-May ANA said a modified Dreamliner had experienced a fault in an electrical panel earlier in the month. But it insisted the glitch was too "minor" to affect the restart of services by the fuel-saving lightweight planes.

ANA operates around a third of the 50 787s that Boeing has delivered, more than half of which have now been put back into service.

Last Monday United Airlines resumed Dreamliner flights with a service from the airline's hub in Houston to Chicago.

Ethiopian Airlines was the first to resume service, in late April, and Air India, which owns six Boeing 787s, also restarted flights last week.

ANA began testing its Dreamliner fleet at the end of April, with a two-hour flight from Haneda Airport in a bid to reassure Japan's consumers the plane was safe.