A helicopter has been dumping water on the flames

Many of those affected also faced the prospect of a second night away from their homes on Friday as the blaze - which is thought to have been started deliberately - continued to rage.

More than 100 firefighters have been tackling the blaze near the village of Wattsville near Risca, and a helicopter has also been used to drop hundreds of gallons of water.

Meanwhile, other fires have also broken out in north Wales - one in Snowdonia and one at Rhiwlas near Bangor, north Wales.

Eighteen pumps from South Wales Fire Service were called to the scene after the Risca blaze was reported late on Thursday evening.

The fire spread over three square miles with flames leaping 50 feet into the air.

Divisional Officer Laurence Edwards said the steep-sided valleys and access problems had made it harder for the crews to tackle the fire.

Police are investigating the cause which is believed to be deliberate South Wales Fire Service spokesman

Residents from forty houses in Wattsville were evacuated to the local workingmen's club as a safety precaution.

Although they were allowed to return home, they were later told they might have to leave again on Friday.

"Three terraces of properties and a children's home were threatened and so an early decision to evacuate was taken," said a fire brigade spokesman on Friday morning.

"It involved some 45 people who were transferred to a local workingmen's club.

"The first call was received yesterday evening and due to the rapid development of the fire the brigade deployed a total of 21 vehicles and 110 firefighters," he added.

More than 100 firefighters have been at the blaze

Police and fire officers have launched a joint investigation into the blaze.

"Police are investigating the cause which is believed to be deliberate," said the spokesman.

"About four square kilometres of standing mature trees are destroyed and a large area of bracken, gorse and shrubs.

"There will be a large brigade presence at the scene for some time to come," he added.

There have been dozens of grass fires across south Wales over the last few days, with the fire service taking up to 1,000 calls a day.

South Wales Police have reiterated that deliberately starting grass fires is a criminal action and offenders will be prosecuted.