A major Sichuan city nearest a massive 'quake lake' threatening to burst its banks issued a detailed emergency plan that may involve the evacuation of up to 1.3 million people. Mianyang , a city of 5.3 million people, had already ordered 158,000 residents of 33 city-administered towns and villages to relocate to surrounding hilltops up to 4km away overnight. This move was a precaution in a best-case scenario - if the weather remains clear next week - where only one third of the lake banks burst, Tan Li, Mianyang's party chief, said yesterday. Another scenario would be a total collapse of the lake barrier, triggering a massive relocation of up to 1.3 million people, he said. 'We're trying hard to aim for the best, but at the same time preparing for the worst-case scenario,' Mr Tan told Xinhua. Nearly 2,000 PLA soldiers and water resources engineers are racing against time to dig a diversion channel to drain the more than 150 million cubic metres of water in the lake. But they would not be able to complete the task until next Thursday, Xinhua said. More than 40 pieces of heavy machinery have been shipped to the site. In addition, two sets of solar lights were installed to ensure relief teams can work around the clock. As of early last night, a 300 metre long channel had been completed, with its widest part at 50 metres, CCTV reported. More than 50 evacuation routes are set out in the emergency plan. All of are no longer than 2km to ensure residents have sufficient time to safely move to higher locations. Every temporary camp on higher ground is equipped with tents, water, food and other necessities, so refugees can sustain themselves for at least 24 hours, according to the plan. Only travel on foot was allowed during an evacuation; vehicles were banned to avoid road jams, Mr Tan said. A team of speedboats is on call to pick up anyone left behind in dangerous situations. 'Our aim is zero casualties,' Mr Tan said. 'We would take all the responsibility if anybody dies in the event of an evacuation.' The Tangjiashan lake was created when landslides caused by the May 12 quake blocked the Jian River above Beichuan town, near the epicentre of China's most destructive earthquake in three decades. The water level in the lake, the biggest of 34 'quake lakes', has kept rising - about 2 metres every day. It rose nearly 1.8 metres by late Tuesday - only 23 metres from the lowest level of the barrier. Fortunately, rain that had been forecast for the area has held off. The Ministry of Finance yesterday allocated 200 million yuan (HK$224.77 million) to tackle the 'quake lakes', 28 of which were still rated as dangerous.