Police and soldiers have cleared the last remaining people from the shadow of a Chilean volcano after a strong explosion spewed glowing-hot rocks from its crater.

The week-old eruption at the Chaiten volcano has scattered ash across a wide swath of South America, closing regional airports and driving more than 7,000 people from their homes. Vulcanologist Luis Lara warned things could get worse.

"The worst that could happen is that the seismic activity begins to increase, the explosions become greater and large domes form that could collapse and produce pyroclastic flows," said Lara, an expert at the government's Geological and Mining Service.