At least 10 people were killed and nine others injured in South Korea after their bus caught fire on a highway, officials said Friday.

The Washington Post reported that twenty people, including the driver, were on the bus when it smashed into the guardrail and caught fire on an expressway near the southeastern city of Ulsan on Thursday night.

Officials said the passengers are retirees of a petrochemical company and their spouses who were returning home from a tour to China.

The exact cause of the fire was under investigation, but authority’s suspect it started after a ruptured tire caused the bus to hit the guardrail, with the friction from the bus sliding sparking flames, according to Ulsan officials.

BDST: 1411 HRS, OCT 14, 2016
NJ/SR