Hwang was in Seongju to try and appease residents who are furious over the joint Seoul-Washington decision to install the Terminal High Altitude Area Defense system, or Thaad, in their town by the end of next year as a deterrent to repeated sabre-rattling by North Korea.
Prime Minister Hwang visited Seongju county on Friday in an attempt to ease their anger.
Some hurled eggs and water bottles, shouting "We oppose (the THAAD deployment) with our lives", according to TV footage. A senior police officer hurt his forehead.
Security guards used boards and umbrellas to shield Hwang and he was quickly taken inside the building. But his suit jacket was tainted by eggs.
Hwang later got out of the bus and into a auto but it too was trapped in the crowd, Yonhap news agency reported.
Meanwhile, praising Washington's recent move to impose sanctions on North Korean leader Kim Jong-un for human rights violations, the three officials agreed to explore "creative" and "effective" measures that could increase pressure on the North related to the issue, the ministry said.
Seongju residents criticized the government for unilaterally deciding on the deployment without consulting them.
Defense Minister Han Min Koo told residents Wednesday he would personally stand in front of the radars to prove they aren't harmful.
North Korea's military on Monday threatened to retaliate against the deployment of the system with a "physical response" once its location and the timing of its installation were decided.
"We strongly condemned the North for its nuclear and missile provocations, while agreeing to beef up our trilateral coordination for the denuclearization of the country", it added.
The agreement came during a trilateral meeting between South Korean First Vice Foreign Minister Lim Sung-nam, U.S. Deputy Secretary of State Antony Blinken and Japanese Vice Foreign Minister Shinsuke Sugiyama in Honolulu, Hawaii, on Thursday (local time), the ministry said in a press release.
Tension on the Korean peninsula has been high since North Korea conducted its fourth nuclear test in January and followed that with a satellite launch and a string of test launches of various missiles. American-led United Nations troops fought alongside South Korea during the 1950-53 Korean War while China assisted North Korea.