Rome, Aug 1 (DPA) Six world records in the evening session at the world championships in the Foro Italico here took the total for the meet to 35.

At the last world championships in Melbourne in 2007, 15 world records were broken in total and with two days of competition remaining, this number has already been more than doubled.

In the evening session Friday the first four swims saw Britta Steffen breaking the women's 100m freestyle record, American Aaron Peirsol winning gold in the men's 200m backstroke in world record time and in the semi-finals of the women's 50m butterfly Marleen Veldhuis and Therese Alshammer taking the world record in consecutive heats.

Serbian Milorad Cavic later broke the men's 100m butterfly world record, before a short lull in setting world records was broken in the final event of the evening by the US men's 4x200m freestyle relay team.

Although Michael Phelps was again beaten by Germany's Paul Biedermann in the opening leg of the relay, the Americans then took control of the race.

Anchor man Ryan Lochte came under pressure from Russia, he managed to hold on to give the US victory in 6:58.55, just one hundredth of a second under their old world record.

For Lochte it was already the third gold medal. He also has a bronze, making him the most successful swimmer at the competition.

Russia took the silver medal, .60 seconds off the pace, while Australia won the bronze with a time of 7:01.65.

Phelps said that when he had seen that he was swimming against the man who beat him in the 200m freestyle in the waiting room, he was not too concerned.

'I think I tried to control it a bit and not just jump in on the first 100. I was not as fast as I would have liked to have been.'

He said that he had seen in the morning that Biedermann had led the German relay team. 'I thought that I would anchor ours, but the coach said from the beginning that I would lead.'

Steffen, who last year took two golds in Beijing, won the one medal that has thus far eluded her when she won the women's 100m freestyle, breaking the world record for the second time in five days.

The 25-year-old won the gold in a time of 55.07, beating the old best mark of 52.22, which she established Sunday as the opening swimmer of the German women's 4x100m freestyle relay swimmer.

Britain's Fran Halsall took the silver medal with a time of 55.87, while Libby Trickett of Australia won the bronze medal with a time of 55.93.

'I am really, really happy. Now anything can happen and I can accept it,' Steffen said as she was hugging members of the German technical staff.

In the very next race Peirsol broke his own men's 200m backstroke world record, winning gold in a time of 1:51.92. His old record stood at 1:53.