TOKYO — The government revised Tuesday the warnings to be issued through the satellite-based J-Alert system if North Korea launches a ballistic missile that could hit Japan, with the initial warning to now call for people at risk to take shelter.

Under the previous alert system, the first warning would merely state that a missile launch had been detected, with the call to take shelter delayed until a second warning.

Government officials said the change reflects forecasts that North Korean missiles could reach Japan minutes after launch.

The new alert system urges people to take shelter “in robust buildings or underground,” while the previous system specified only sheltering “indoors.”

In the event a missile passes over or near Japan, the new alert system calls for people who spot potential fallen missile fragments to stay away from them and notify authorities.

The J-Alert system, which relays information from the central government to local authorities, is also used for natural disasters.

North Korea most recently test-fired a ballistic missile on April 29, in a launch the South Korean military described as a failure.