The surface of Spain’s La Palma island is continuing to expand as lava from a volcano flows into the Atlantic Ocean and hardens as it comes into contact with water, scientists have said.

Copernicus, the European Union’s Earth observation programme, said on Thursday that its satellite imagery showed a D-shaped tongue of molten rock building up on the island’s western shore measured 338 hectares (835 acres) by the end of Wednesday.

Trade winds typical of Spain’s Canary Islands were helping dispel the plumes of water vapour and toxic gases that result when the lava, with a temperature of over 1,000C (1,800F), meets the ocean, where the water is 22C (71.6F).

But authorities were on alert as Spain’s weather forecaster, AEMET, indicated that the wind’s direction could change later on Thursday and bring the toxic plumes towards the shore and further inland.

The hydrochloric acid and tiny particles of volcanic glass released into the air can cause skin, eye and respiratory tract irritation.

The direction the lava flow could take was also a source of concern.

Molten fluid emanating from the volcano that first erupted on September 19 was still running downhill like a river and tumbling over a cliff into the Atlantic.

But uneven terrain could make the lava overflow its current path, spread to other areas, and destroy more houses and farmland.

At least 855 buildings and 19 miles (30km) of roads, as well as other key infrastructure, have been wiped out so far.

Banana plantations that are the source of income for many islanders have also been either destroyed or damaged by volcanic ash.

More than 6,000 residents have been evacuated so far, and hundreds more were advised to stay at home to avoid the possible inhalation of toxic gases.

No casualties or injuries have been reported among La Palma residents since the eruption began.

La Palma, home to about 85,000 people, is part of the volcanic Canary Islands, an archipelago off northwest Africa. The island is roughly 22 miles (35km) long and 12 miles (20km) wide at its broadest point.