Last minute preparations took place earlier in the week
Racegoers are being urged to use public transport to get to Aintree racecourse as the 161st Grand National festival gets under way in Liverpool.
About 150,000 people are expected to attend the three-day event and police are warning the area will become heavily congested.
People are being urged to use trains, taxis or local park-and-ride services to avoid traffic delays.
The Grand National steeplechase takes place on Saturday, on the final day.
Ch Supt Mark Matthews said: "Merseyside Police would encourage race goers to travel to the event by public transport where possible to avoid congestion and parking problems.
"I would like to thank the public in anticipation of their cooperation for what promises to be a memorable and enjoyable event."
Organisers have spent the last few days putting the finishing touches to the course ahead of the first day of the festival on Thursday.
Racegoers should be most comfortable on the first day, which was forecast to be the warmest of the three with maximum temperatures of 13c.
Ladies' Day, which takes place on Friday, could see light showers and a north-westerly breeze spoiling the renowned outfits of racegoers.
Colder weather is expected for the final day on Saturday, with a 9c maximum temperature and possible hail and sleet showers.
Favourites for the steeplechase include Cloudy Lane, Slim Pickings and Comply or Die.
The winning horse will race four miles and jump 30 fences around the Aintree course before crossing the line.