Brighton Pride 'more important than ever'
Up to 300,000 people are taking part in Brighton's Pride celebrations, which organisers have said are "more important then ever".
Security is tight at the event after terror attacks overseas, and a minute's silence is being held for victims of the Orlando shootings in the US.
Director Paul Kemp urged all allies and friends of the LGBT community to stand "shoulder to shoulder".
The carnival parade started at Hove Lawns.
Mr Kemp said: "Despite the advances of equality and equal marriage in the UK, the recent horrific event in Orlando and continuing attacks on LGBT people and communities globally have highlighted there's still a long way to go.
"Brighton Pride 2016 will be more important that ever and I ask all allies and friends of the LGBT community to come out and stand shoulder to shoulder with friends and family to stand up against all hate crime."
The one minute silence is being held at 19:00 BST.
Mr Kemp said the country remained on high alert after recent events but the information from Sussex Police was the threat to Brighton Pride was "moderate".
"Of course, we ask the public to be vigilant and there are extra security measures," he said.
He said over a thousand trained security staff would be at the event but the public were the "eyes and ears".
At Pride: BBC South East reporter Lucinda Adam
The parade and the party is well under way in glorious sunshine. There are thousands of people coming out to celebrate their sexuality.
We've got people dressed up. We've got floats - and up to 300,000 people lining the parade route.
There is tight security this year because of recent world events, with armed officers on the street and concrete barriers along part of the route.
But that's not going to deter them from having fun today. The mood here is defiant and one of a party atmosphere.
Mr Kemp said: "It's really down to the public. If they're coming to Pride, if they've got a bag with them for example, don't leave a bag around. It's common sense stuff."
Adding that Pride in Brighton had gone beyond an LGBT festival, he said: "Pride in Brighton and Hove is a celebration of diversity for all our communities.
"Families come along to the parade. Everyone gets involved. It's a great celebration."
He also said this year's festival - attended by people from countries around the world including Brazil, Chile, Argentina, China and Australia - would bring £18m into the local economy.
Following a Southern rail warning about travel disruption, Mr Kemp said Thameslink trains were running and there would be a train service in and out of Brighton for people to attend the event.
Southern rail said services would be busy and some may be altered or replaced by buses. Preston Park station is closed and there is a queuing system at Brighton station.