LG Electronics has offered free replacement batteries after two users claimed that their notebook PCs exploded.

Despite the recall offer, LG has so far described the incidents as "isolated ".

The partial recall applies to batteries manufactured by LG Chemical for two recent notebook models, the Z1 and Z2.

Video shot in January showed a journalist's Z1-AE007 notebook PC burning and then exploding.

LG stopped selling the Z1 last week after a second battery fire was reported, according to South Korea's Yonhap News Agency.

The first battery fire was triggered by "unusual heat and pressure", a researcher from the Korea Electrotechnology Research Institute told the Korea Times.

However, the researchers were unable to discover how that battery had got into such a state.

The notebook's owner claimed that it had been put into a backpack in sleep mode a short while before catching fire, and that there was nothing unusual about the storage conditions.

Common safety standards call for Lithium-based batteries to withstand at least 10 minutes at 130 degrees centigrade.

LG ascribed the explosion to "an external shock at an extremely high temperature", according to the Joongang Daily.

In related news, a Samsung Electronics notebook PC was reported to have caught fire in Seoul last week. The company claimed that the battery may have overheated when air vents were blocked.

In the world's most expensive battery recall, Sony paid more than $400m to replace more than 10 million potentially-faulty notebook batteries during 2006.