NEW DELHI (AFP) Delhis besieged Commonwealth Games confronted a new enemy on Thursday when over 50 swimmers fell ill just as eyes turned to the 100m, the traditional blue riband track and field showdown. Around 40 English and 12 Australian swimmers had complained of feeling unwell after competing at the S.P. Mukherjee Aquatics Complex, with team officials insisting that the problem area was the warm-up pool. We must investigate this immediately. If the water is unsafe then clearly you cant swim in it, said Commonwealth Games Federation president Mike Fennell. We are concerned if athletes cant perform to their best. Stomach problems being experienced by swimmers have already forced two Australian medal prospects to pull out. Olympic bronze medallists Andrew Lauterstein and Hayden Stoeckel failed to start in the 100m butterfly and 100m backstroke heats because of gastro problems, a team spokesman told AFP. The problems in the pool are the latest to plague these ill-starred Games after the build-up was marred by allegations of corruption, terrorism fears, shoddy workmanship and big-name withdrawals. Since the Games got underway, venues have been scarred by acres of empty seats despite assurances from organisers that ticket sales have boomed. Under-fire organising committee chairman Suresh Kalmadi insisted on Thursday that 125,000 tickets had been sold the previous day. There has been a real surge, he said, before claiming that tickets for the rugby sevens, swimming as the semi-finals and final of the badminton are sold out. Kalmadi said that 90 percent of boxing tickets have already been sold and 80 percent of the tennis. On a day when 35 golds are to be decided, the all-conquering Australian swimming squad were out for more gold to add to the 14 they had already garnered. Former world record-hodler Eamon Sullivan was fastest into the final of the mens 100m freestyle while compatriot Emily Seebohm goes for the one-two in the 50m backstroke following her gold in the 100m. Olympic champion and Commonwealth record holder Leisel Jones is looking to defend her 100m breaststroke crown for a third consecutive Games after her success in the 200m on Wednesday. Englands world record holder and Olympic champion Rebecca Adlington is favourite for the 800m final while, in the mens 50m breaststroke, world record holder and world champion Cameron Van Der Burgh of South Africa is seeking a double after winning the 100m event. Inside a virtually deserted Jawaharlal Nehru athletics stadium, Kenyas Viola Kibiwot was the fastest into the womens 1,500m final with compatriot and Olympic champion Nancy Langat also easing through. Other gold medals at stake on Thursday are in the mens and womens 100m. In the absence of Usain Bolt and Asafa Powell, Englands Mark Lewis-Francis, who won silver in the European Championships, Jamaicas Oshane Bailey and Canadas Sam Effah look to be the best bets for gold. The womens 100m final is also held, with Natasha Mayers of St Vincent and the Grenadines the fastest into the semi-finals but well off Debbie Fergusons Commonwealth record time of 10.91. Other medals will be decided in the womens hammer, where Wales Carys Parry (63.53m) was the best qualifier, and mens shot put, with Amand Scott of Jamaica among the favourites. In early medal action on Thursday, Australia continued to dominate track cycling with teenager Megan Dunn picking up her second gold medal in as many days in the 10km scratch race. Australia now have seven from a possible eight track titles and look unstoppable with three more golds up for grabs on Thursday.