South Korea has raised its earthquake alert level to "caution" after a four-point-five magnitude earthquake occurred in waters off the east coast early Monday morning. 

It is the strongest tremor to hit the Korean Peninsula so far this year. 

An interior ministry official urged the public to familiarize themselves with responses to unexpected situations and encouraged institutions to review responsibilities in accordance with the crisis management manual in case of an earthquake.

The ministry plans to strengthen its follow-up situation management by operating an emergency response team led by the earthquake response department.

It had issued the "attention" level, the lowest on the four-tier alert system, on April 25 following a series of tremors.

As of 11 a.m. on Monday, there were 21 reports by people who felt the quake, but no reports of damage or casualties have come in so far.