The parade features a range of floats, vintage vehicles, carnival costumes and an Irish dragon Some 80,000 people are expected to take part in St Patrick's Day celebrations in Birmingham in what is thought to be the biggest event of its kind in the UK.
The city, which has a large Irish community, has hosted an annual St Patrick's parade every year since 1996.
This year's parade, centred around Digbeth, was delayed after a crash on the M6 caused congestion into the city.
Live music, street fairs and a market are also planned.
This year's theme is Irish myths and legends.
The parade, which features hundreds of floats, vintage vehicles, carnival costumes and an Irish dragon, is due to end at 14:00.
Michael Grimes, a student at the University of Birmingham, said the city had a "huge Irish culture".
"Derry's a good craic on St Patrick's Day, but nothing like this. This is ridiculous," he said.
Organisers praised the good weather and said the crowd could be the biggest ever.
'Built Birmingham' It will also see road closures around Bradford Street, Birchall Street, Chapel House, Stoneyard and Green Street until 16:00, although closures around the Irish Centre will remain in place until 18:00.
The Birmingham St Patrick's Day celebrations are believed to be the third largest in the world, after New York and Dublin.
Birmingham Library is being lit up in green over the weekend to mark the city's Irish connections.
With an Irish quarter and an Irish Centre, as well as community groups, organisers said Irish immigrants had made a big impact on Birmingham over the years.
"They helped to build Birmingham for a start," Anne Tighe, head of the festival committee, said.
"All immigrants, including the Irish, have had an impact on the city and we're welcoming everyone to come and celebrate St Patrick's Day with us."