LOS LLANOS DE ARIDANE, CANARY ISLANDS -- A volcano that has already destroyed nearly 1,000 buildings on a Spanish island increased its explosive power Tuesday, roaring louder and spewing thicker lava out of its main vent.

The volcanic eruption started on Sept. 19 and has forced the evacuation of over 6,000 residents of the island of La Palma in the Canary Islands archipelago off the northwest coast of Africa.

Some 946 houses have been completely destroyed and nearly 100 more affected, while farmers are struggling to keep the surviving banana plantations irrigated after lava flows destroyed roads and water pipes.

The Canary Islands Volcanology Institute, Involcan, said Tuesday that activity in the La Palma volcano had become "explosive, with falling pyroclasts and bombs."

A video released by the institute the night before showed a block of molten rock that, according to the institute, had hit against a wall more than 1 kilometre (0.7 miles) away from the vent, a sign of the explosive activity of the volcano.

According to Involcan's calculations, the volcano has emitted at least 250,000 tons of sulfur dioxide and 35 million cubic meters of magma.

Cameras captured with detail the thicker lava that emerged from the main vent in greater quantities after the surrounding cone collapsed again on Monday. Experts were closely watching if the downhill path of the lava will follow the previous flows or if it will expand into other areas -- spreading its destruction.

After meandering for 6 kilometres (nearly 4 miles), the lava has been tumbling since last Friday to the Atlantic Ocean. By Tuesday, a peninsula that has been forming has extended the island by 30 hectares (74 acres), or the equivalent of about 42 soccer fields.

The island's tourism chief, Raul Camacho, said Tuesday the island remained open for tourists, calling on visitors to keep arriving despite the eruption because their spending is needed to revive the local economy.

La Palma, Camacho said, "is a safe island where there is life, where pupils go to school, where the baker keeps delivering bread every day."

He said areas affected by the volcano were about 10% of the island.

"Life is normal in the rest of the island," he added.