© Dave Porter/Getty ImagesPolice reportedly cleared Worthing pier and the surrounding area.
A cordon was set up, a section of the beach was evacuated and people were told to avoid the area and close their doors and windows.
Tim Loughton, the MP for East Worthing and Shoreham, tweeted that an investigation had been launched in response to reports of "bathers affected by some sort of chemical type irritants". The incident took place around midday.
Sussex police said: "A small number of people have reported symptoms including sore eyes and vomiting, two of whom were taken to hospital. They have both since been discharged, and advised to go home, wash their clothes and have a shower.
"Anyone else affected is advised to do the same, and use copious amounts of water to wash your eyes."
A staff member at Coast Cafe said earlier that people had been calm but that "a couple of people were complaining of itchy eyes".
She said: "They've cleared the seafront and we've got the windows closed and are locked in."
The former windsurfing world champion and Olympian Christine Johnston was on the beach preparing kitesurfing lessons at 12.15pm when a beach patrol told her and her students to leave.
"They came along on their buggy and said we should leave with immediate effect because there had been an incident," she said. "They said a few people had been hospitalised. They were covering their mouths with clothing.
"I did ask [what was happening] but they wouldn't comment. They told us they were going to go down the area affected, between Lancing and Worthing. We went up to the cafe and saw quite a lot of movement of police cars and an ambulance.
"My eyes were a bit sore and itchy, and a friend who was on the beach said she felt her eyes were sore too."
Comment: As of Monday, the cause of the incident remains unexplained.
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