Two brothers were taken to hospital after the waterbike they were riding collided with a speedboat.

It is believed an 18-year-old suffered serious head injuries and a ten-year-old boy broke his arm in the crash near Bognor pier on Saturday.

Onlookers reported the waterbike and 18ft-long Fletcher speedboat, which had four people from Bognor aboard, colliding at about 20mph shortly before 2.30pm.

Police said no one was to blame for the accident, which was witnessed by members of the victims' family, who were on the beach.

The brothers, who have not been named, are believed to be from the Wimbledon area of London and were staying at a caravan park near Bognor.

They were taken to St Richard's Hospital in Chichester. Police said their injuries were not thought to be life threatening.

A police spokesman said: "The family was enjoying a day out by the seaside. We questioned witnesses to establish if there was any culpability but it appears to be an accident."

Coastguards dealt with a series of minor incidents during the weekend as thousands of people flocked to the beaches to make the most of the hot weather.

Littlehampton lifeboat was launched amid fears that two children on inflatables were being swept out to sea but beach office staff reached them in time.

After a poor June and July, major roads to the coast were jammed with traffic, delighting Brighton traders.

Peter Avey, who runs the Seasiders amusement arcade and restaurant on the lower promenade, said: "This weather has saved our lives, it was getting a bit desperate."

Seafront officer David Wheeler said: "You would be hard pushed to spot any stones. Pretty much the whole beach has been taken up with people.

"The traders seem happy and the lifeguard teams have been out a lot but mostly to prevent incidents rather than responding to them."

The M23, the A259 and the A27 were packed as people in London and the Home Counties left for the coast.

An AA Roadwatch spokesman said: "Lunchtime on Saturday was the worst period with very heavy traffic. It did improve during the afternoon but the coastal roads were heavy going."

In Eastbourne, people packed the pier and the seafront, causing jams between Prince's Park and the Cavendish Hotel as temperatures soared into the mid-eighties.

Worthing beach officer Tony Adams said: "It has been a very busy couple of days, with a lot of people on the beach but also a lot of craft in the water."

The emergency services in East and West Sussex reported several weather-related incidents.

In West Sussex, firefighters were called to several field fires as parched undergrowth caught light.