South Korea says a massive explosion in North Korea's border town of Ryongchon Thursday is estimated to have killed or injured between 700 to 800 people, significantly lower than earlier estimates of 3,000 casualties.

Amid conflicting reports, a South Korean official said the blast had occurred at around 2:00 p.m. Thursday, when a train carrying three 60,000-liter tanks of liquified petroleum gas had stopped at Ryongchon station.

The city and its railway station, which serves as a transportation hub near the border with China, is a stop-over for trains delivering fuel from a nearby oil processing plant.

Sources said, meanwhile, that satellite images showed a crater with a diameter of 150 meters at the blast site, and that surrounding areas within a 600-meter radius had been damaged.

So far, the North Korean media has remained silent on the explosion.