GRUENHEIDE, Germany, Oct 9 (Reuters) - The first cars to emerge from Tesla"s new Berlin factory should roll off the production line as early as next month, CEO Elon Musk said at the site of the plant on Saturday, but added that volume production would take much longer to achieve. Musk hopes to get the green light in coming weeks to start production at the site. The latest consultation on public concerns towards the site closes on Oct. 14, after which the Environment Ministry will make a decision. "Starting production is nice, but volume production is the hard part," Musk told a cheering audience at a festival at the plant site, many of whom livestreamed the speech on social media. "It will take longer to reach volume production than it took to build the factory." He said volume production would amount to 5,000 or "hopefully 10,000" vehicles per day, and battery cells would be made there in volume by the end of next year. He also defended the factory against critics of its environmental impact, saying that it used "relatively little" water and that battery cell production was "sustainable". Some local residents and environmental groups are unhappy with Musk"s approach, which they say flies in the face of German business culture. read more "I would tell him to stop building electrocars but rather fly to Mars," said Manu Hoyer, who led a small protest of locals who oppose the project on environmental grounds, saying it will pollute drinking water. Brandenburg"s economy minister has put the chances of the factory gaining approval to operate at 95%. Tesla has submitted plans to invest 5 billion euros ($5.8 billion) in a battery plant with 50 GWh capacity next to the site, outstripping Volkswagen"s (VOWG_p.DE) planned 40GWh capacity site in Salzgitter. read more Musk said Tesla was worried that recruiting sufficient staff would be an issue, calling for people to apply from "all over Europe". He said he hoped the battery plant would reach volume production by the end of next year. POPSTAR RECEPTION The company offered 9,000 tickets to the festival, with residents of Brandenburg state given priority. "Look, Mummy! A Tesla," shouted an excited 9-year old called Emil, one of many children lined up with parents waiting for a 90-minute site tour. Fans cheered and laughed when Musk took the stage at sunset, welcoming him like a popstar. "This day is unique," said Tesla fan Fred Schroeder. "The Tesla factory in Germany will be opened to the public for the first time. That is a very special day." Another had driven his Tesla from Milton Keynes in Britain, despite not having a ticket. He said it was worth it just to see the site from the outside. ($1 = 0.8649 euros)