American gymnast Biles flies high as Serena crashes out

American gymnast Simone Biles made a flying start to her bid for a record five Rio Olympic gold medals on Tuesday as Serena Williams crashed out of what could be her final Games.

Elsewhere an official media bus came under attack from either gunfire or hurled stones, in the latest security scare for the tournament.

Biles, tipped as the biggest thing since Nadia Comaneci, helped the USA cruise to women's team victory by eight points over Russia, kick-starting her bid for an unprecedented five titles.

"It's everything and more than I'd hoped it to be," said the tiny Biles, 19, who has set gymnastics alight in with 10 world titles in the past three years.

"It didn't feel like the Olympics. That helped us," said the 1.45m (4ft 9ins) Texan. "It felt like one more routine and we kept calm."

Biles' life story is Hollywood material after she was adopted and raised by her grandparents from the age of three as her mother struggled with drug and alcohol addiction.

As her Olympic odyssey got underway, another crumbled as defending tennis champion Williams suffered a shock 6-4, 6-3 defeat to Ukraine's Elina Svitolina in the third round.

Williams, hampered by a shoulder injury, served five double faults in one game of the second set as her own bid to reach five gold medals ended.

The 34-year-old and her sister Venus were earlier knocked out of the women's doubles, the three-time champions' first ever defeat together in Olympic competition.

"It was a great opportunity. It didn't work out the way I wanted it to, but at least I was able to make it to Rio. That was one of my goals," she said.

French Open champion Garbine Muguruza also crashed out, losing 6-1, 6-1 to Monica Puig of Puerto Rico.

Green water

It remained unclear whether gunfire or stones were used in the media bus attack, which smashed windows and injured one journalist, according to a report.

The incident comes after a stray bullet ripped through a media tent at the equestrian venue and a controlled explosion near the finish of the men's cycle road race.

In diving, competitors were perplexed to find the water had turned inexplicably from light blue to green overnight, although organisers insisted it was safe.

China's Chen Ruolin shrugged off the colour-change to claim a record-equalling fifth gold medal in the women's synchronised 10m platform, with partner Liu Huixia.

Earlier Olympics officials promised to push for life bans for dope cheats echoing calls from Michael Phelps and Michael Johnson.

After Phelps said he was angry that convicted dopers were allowed to compete, the International Olympic Committee (IOC) said its president Thomas Bach backed lifetime suspensions from the Games.

Doping has cast a long shadow over the Rio Olympics after a row over the participation of Russia since revelations of a state-orchestrated drugs regime.

New Zealand's rugby hopes took a blow when superstar Sonny Bill Williams suffered a tournament-ending injury in their shock 14-12 opening defeat to Japan.

France won their first gold of Rio in the equestrian team eventing. French hero Astier Nicolas also took a silver in the individual event behind Germany's Michael Jung.

Chinese weightlifter Deng Wei won the women's 63kg category with a world record after Taiwanese rival Lin Tzu-chi pulled out amid reports of a failed dope test.

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