A huge operation is under way to rescue 40 construction workers trapped after a tunnel partially collapsed in the Indian state of Uttarakhand. The entrance to the Silkyara tunnel, which was under construction as part of a road project in Uttarkashi district, collapsed in the early hours of Sunday morning while dozens of workers were inside. On Monday, officials said contact had been made with the trapped workers using walkie talkies, and that all those inside were alive. Funnels were inserted through the collapsed construction to get them oxygen and compressed food packets. The workers are said to have about eight to 10 hours left before the oxygen in the tunnel runs out. Most of those stuck inside were migrant labourers from across the country. “Everyone is safe, we are in constant touch with the trapped workers,” said Prashant Kumar, a state official. The rescue effort, overseen by police and the state disaster response force, moved into its second day on Monday as several excavators and heavy machinery worked to move the heavy rubble and debris. Officials said more than 20 metres of concrete rubble and twisted metal had been removed, but a further 35 metres needed to be cleared to reach those stuck inside. The Uttarakhand chief minister, Pushkar Dhami, arrived at the scene on Monday and said the Indian prime minister, Narendra Modi, had promised “all possible help” for those trapped inside. “We hope they will be rescued soon,” he said. The tunnel is part of the 900km Char Dam road project, which aims to improve connectivity across the mountainous terrain of the Himalayas in Uttarakhand. The project has proved controversial and faced various legal challenges from environmentalists and locals as it involves drilling vast tunnels into the fragile Himalayan landscape, and has been associated with issues of subsidence, landslides and erosion of forests and local ecology.