More than 29,000 participants have signed up for Sunday’s Cardiff Half Marathon, making 2024 its “biggest year ever”, according to organisers.

Widespread road closures are in place to accommodate the 13.1 mile (21km) route, with racers setting off from 09:50 BST.

Cardiff council said the city would be “exceptionally busy” and advised residents and visitors to plan ahead.

Transport for Wales (TfW) is providing additional train services to bring runners and spectators into the capital ahead of the race, but some other rail routes will be disrupted due to engineering works.

“This is our biggest year ever with over 29,000 people registered to take part across the weekend,” said Matt Newman, chief executive of Run4Wales.

The race start-time is staggered, with the wheelchair race from 09:50 BST.

Runners in the elite, white, green and red pens began at 10:00, while runners in the yellow and blue pens got going at 10:10.

The race began on Castle Street, continuing past the Principality Stadium and Cardiff City Stadium to Penarth.

The runners then cross the barrage back to Cardiff Bay, before looping around Roath Park Lake and finishing in the civic centre.

There is an extensive set of road closures in place across Cardiff.

Closed until 00:00 on 7 October:

• College Road from the junction with Museum Avenue to the junction with King Edward VII Avenue
• Edward VII Avenue to the junction with Boulevard de Nantes and to the junction with City Hall Road

Closed until 10:45 on 7 October:

• North Road from its junction with Colum Road to its junction with Boulevard de Nantes

Closed between 04:00 and 12:00 on 6 October:

• North Road south of the junction with Boulevard de Nantes to the junction with the A4161
• The A4161 from the junction with North Road to its junction with Kingsway
• Kingsway from the junction with the A4161 to the junction with Duke Street
• Duke Street and Castle Street
• Cowbridge Road East from the junction with Castle Street to the junction with Cathedral Road

Closed between 10:00 and 15:10 on 6 October:

• Colum Road
• Park Place from the junction with St Andrews Place to the junction with Colum Road

Closed between 08:30 and 15:10 on 6 October:

• Cowbridge Road East from the junction with Cathedral Road to the junction with Neville Street
• Wellington Street, Leckwith Road and Sloper Road
• Penarth Road, Cardiff Bay Barrage, Harbour Drive and Roald Dahl Plas
• Britannia Quay, Pierhead Street, Bute Place, Lloyd George Avenue
• Herbert Street, Tyndall Street, East Tyndall Street and Windsor Road
• Adam Street, Fitzalan Place going across Newport Road
• West Grove, Richmond Road and Albany Road
• Marlborough Road, Blenheim Road, Pen-Y-Lan Road and Ninian Road
• Fairoak Road, Lake Road East and Lake Road West
• Fairoak Road, Cathays Terrace, Corbett Road and Museum Avenue

More information, including access arrangements for residents, can be found on the Cardiff council website.

TfW ran additional early morning trains to help runners and spectators get into Cardiff in time for the race.

People travelling from Swansea, Hereford, Maesteg, Gloucester, Ebbw Vale, Barry Island, Penarth, Radyr and Rhymney were able to catch a train bringing them into the city centre before 09:00.

Engineering works have closed the lines between Treherbert, Aberdare, Merthyr Tydfil and Radyr, but there will be rail replacement buses to connect with trains at Radyr.

Engineering works are also taking place on the Vale of Glamorgan line, but TfW said customers from Llantwit Major and Rhoose could use a replacement bus to Barry or Bridgend stations.

For motorists, a park and ride facility at Cardiff City Stadium, opens between 07:00 and 18:00 on Sunday.

Cardiff Bus also ran a number of buses into the city centre prior to start of the race, outlined on its website.

Race organisers provide a number of “spectator zones” at various points along the route for the thousands who turn out to watch the race in person.

These zones are on Castle Street, Corbett Road and King Edward VII Avenue, where the runners cross the finish line.

You can also watch the highlights from the half marathon on BBC iPlayer and S4C, from 20:00 on 7 October.

Runners are told they must complete the 13.1 mile race in 4.5 hours, which is around the average walking pace.

If runners fall behind the required pace to finish in this time, a sweep vehicle will collect them.

Run4Wales said those who wish to continue after the race has ended should do so on the pavement, as roads re-open, and do so at their own risk.

Race organisers have said runners should avoid wearing headphones during the race to limit the risk of injury to themselves and others.