SEOUL - South Korea reported 583 new coronavirus cases on Thursday, the highest since March, as it grapples with a third wave of infections that appears to be worsening despite tough new social distancing measures.

The government reimposed strict social distancing rules on Seoul and surrounding regions this week, only a month after they had been eased following the second wave of infections.

Now some experts say the government moved too early to relax those rules, as the daily official case tally exceeds 500 for the first time since March 6.

"The easing was done because of economic concerns and growing fatigue but it was premature and sowed the seeds of people's complacency," said Kim Woo-joo, a professor of infectious diseases at Korea University Guro Hospital in Seoul.

South Korea's first wave emerged in late February from meetings of a religious sect but the latest cases are more dispersed around the capital Seoul, making them harder to trace and contain.

The armed forces ordered a 10-day ban on leave after a series of outbreaks at military facilities. Other clusters have been traced to a sauna, a high school, an aerobic academy, churches, a children's cafe and a friends' get-together.

"COVID-19 has arrived right beside you and your family," Health Minister Park Neung-hoo told a televised meeting of health officials.

"In particular, the spread of infections among young generations is extraordinary."

Infections among young people, many of whom show no symptoms, prompted the government to urge students to stop attending cram schools and private lessons ahead of college entrance exams slated for Dec. 3.

"Infections are emerging concurrently in our daily lives including family gatherings and informal get-togethers which makes it difficult for the government to take preemptive action," Education Minister Yoo Eun-hae told a briefing.

Health officials did not respond directly to criticism that the government had been too quick to ease restrictions following the previous spike in infections in August.

They have expressed regret about the economic impact of the latest measures, coming just after Asia's fourth-largest economy returned to growth in the third quarter. 

South Korean markets held their nerve on Thursday as the central bank kept its policy rate steady and marginally raised its growth outlook for this year and next. 

Of the latest cases, 553 were locally transmitted and almost 73% of those were in the greater Seoul area, the Korea Centers for Disease Control and Prevention (KCDC) said.

Total infections in South Korea stand at 32,318, with 515 deaths.

(Reporting by Hyonhee Shin; Additional reporting by Sangmi Cha; Editing by Stephen Coates) ((hyonhee.shin@thomsonreuters.com; 822 3704 5658;))