TOKYO -- Japan Airlines says a San Francisco-bound Boeing 777 returned to Tokyo after a warning flashed in the cockpit saying the jet's hydraulic level was low.

The company says the plane carrying 236 passengers and 13 crew had departed around midnight Tuesday and returned about four hours later to Tokyo's Haneda airport. There passengers boarded another plane that departed for San Francisco and arrived there safely early Tuesday local time.

The company says mechanics found a leak in the hydraulic system of the plane that remained in Tokyo.

The incident happened after an Asiana Airlines Boeing 777 crash-landed Saturday in San Francisco, killing two. The cause of the crash is not yet known.