A pregnant mother screamed and ran after a man who snatched her two-year-old son in a playground.
She followed the man, pushing a buggy carrying her other child, and shouted for him to let the boy go.
The pursuit lasted several minutes before the man put the boy down and fled. The terrified child ran to his mother.
Police searched the area but there was no trace of the offender. Officers were carrying out house-to-house inquiries today.
It happened at 10.50am on Friday in a playground in Saltdean Park, Saltdean.
The boy had wandered a short distance from his mother when she saw the man pick him up.
She told police: "I shouted loudly but he started walking away quickly. I screamed at the top of my voice."
Detective Inspector Chris Standard, of Brighton and Hove CID, said: "We are treating this incident very seriously and we have a team of officers working on the case.
"We are not sure whether this man has mental health problems or whether this was something more sinister."
Police are anxious to trace witnesses in the park, especially a woman of about 70 who spoke with the mother before the abduction. She had greying brown hair and wore a long coat.
Officers also want to talk to an elderly couple seen nearby with what appeared to be their grandchildren.
The offender was white, 35 to 40, 5ft 10in tall and had black hair. He wore a dark blue knitted sweater and dark blue cotton trousers.
Anyone with information should contact Detective Sergeant Emma Dymond of Brighton and Hove police on 0845 6070999 ext 50513.
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