LA PALMA, Sept 24 (Reuters) - Intensifying volcanic explosions on the Spanish island of La Palma forced firefighters to retreat and authorities to evacuate three more towns on Friday, while airlines cancelled flights due to a cloud of gas and ash,the biggest since the volcano erupted. Firefighters pulled out of clean-up work in the town of Todoque on Friday afternoon as a new vent opened up in the flank of the volcano and videos shared on social media showed a massive shockwave emanating from the eruption site. A Reuters witness saw a huge grey cloud billowing from the top of the volcano on Friday afternoon, the largest since the eruption began on Sunday. "The volcano is in a newly explosive phase ... Firefighters will not operate anymore today," tweeted the Tenerife fire service, which has been deployed to help on La Palma. Authorities ordered the evacuation of the towns of Tajuya, Tacande de Abajo and the part of Tacande de Arriba that had not already been evacuated on Friday afternoon, with residents told to assemble at the local football ground. Canary Islands emergency services had initially told residents to stay indoors to avoid the dense cloud of ash and lava fragments but later decided to evacuate due to the heightened risk from explosions. It wasn"t just people being evacuated, but animals too. "The evacuation of people is the main priority ... although there are also other important tasks such as keeping pets safe," the Guardia Civil tweeted, with a video showing officers carrying reluctant goats to safety. Since erupting on Sunday, the Cumbre Vieja volcano has spewed out thousands of tons of lava, destroyed hundreds of houses and forced the evacuation of thousands of people. loading No serious injuries or fatalities have been reported but about 15% of the island"s economically crucial banana crop could be at risk, jeopardising thousands of jobs. Canary Island airline Binter said on Friday it had cancelled all flights to La Palma due to the volcano eruption, while Iberia (ICAG.L) cancelled its only flight scheduled for the day, and another local airline, Canaryfly, also suspended operations. Binter said it was forced to halt operations to and from La Palma as the ash cloud had worsened considerably in the last few hours. The airline, which had initially only cancelled night flights, could not say when it would resume operations. A cloud of toxic gas and ash extends more than 4 km (2-1/2 miles) into the sky, the Canaries volcanology institute said on Thursday. It has begun to drift northeast towards the Mediterranean and Spanish mainland, the national weather agency said. Airspace above the island remains open apart from two small areas near the eruption site.