(AFP) - Deadly attacks such as those inflicted in Belgium have become part of the new normal for athletes whose travels to make money can put them in jeopardy.

"It's just a really dangerous time in the world right now," women's tennis world No. 1 Serena Williams said on Tuesday.

"You can be anywhere in the world and something can happen. We should all have to be kind of on alert. No city is safe at this point. You have to be alert."

The 21-time Grand Slam singles champion, top seed for the ATP and WTA Miami Open that began on Tuesday, said people cannot just set aside the tragedy but must be attentive for those with bad intentions as well as mourn for the dead and injured.

"You just have to pray for the people involved and their families," she said.

Australian Open champion Angelique Kerber of Germany called the attacks "really sad and terrible" and noted how tough it is to shake off the effects of such bombings and continue on with the life of a global travelling tennis star.

"Sometimes you are thinking you travel every week," Kerber said.

"Sometimes it seems hard. But at the end, you have no choice."

Two-time Wimbledon champion Petra Kvitova of the Czech Republic said that she refuses to surrender to fear.

"We can't (worry). We can't do anything about that," Kvitova said.

"It's very sad news to wake up to. As a European, it's tough. When they open the border, it's hard to close it again.

"I think people could be nicer. Maybe one day."

Swiss two-time Grand Slam champion Stan Wawrinka says terrorist incidents also make it harder to leave home for the next event.

"When you travel you have to put that aside but for sure that's a tough way to travel," Wawrinka said.

"It's really sad what has happened. When you say that, it's sad for all the people and families and friends. It's tough."

Poland's Agnieszka Radwanska says sometimes things that happen far away leave the most unnerving impression.

"Those kind of things happen far from us, they are always scary," she said.

Spain's Carla Suarez Navarro takes inspiration from such tragedy to make sure she lives each day to the fullest, knowing the next is never guaranteed.

"It's sad to hear about the events in Brussels. You never know what is going to happen," she said.

"We have to enjoy the life because you never know what's going to come."