Thousands of letters have poured in from around the world addressed to a young Nova Scotia boy with autism, after his older sister launched a Facebook campaign asking strangers to send him mail for his birthday.

Kristian Hayes celebrated his 11th birthday on Wednesday at the Stellarton, N.S., post office. He shared a birthday cake with his family and was also presented with 600 letters, adding to the pile of 3,500 letters he has already received over the past few weeks.

"(My sister) gave me presents," Kristian told CTV Atlantic. "She was there for me and I love her."

The letters started coming in last month when Kaitlyn Hayes posted a picture on Facebook, asking people to send her little brother letters for his birthday. The photo, which shows Kaitlyn holding a handwritten poster, was later posted on the Firefighters vs Autism Facebook page and has been shared more than 7,600 times.

"My little brother is turning 11 years old on Sept. 2," the poster says. "He loves getting mail and collects stamps. Even if you do not know him, please make my little brother happy!"

The siblings' mother, Heidi Hayes, says Kaitlyn's goal was to receive 50 letters. But soon after posting the photo on Facebook, thousands of letters started coming in from around the world.

"They've come from the United Kingdom, Australia, France, Netherlands – everywhere you can imagine, we've had mail from (there)," Hayes said.

According to Kaitlyn, her younger brother asks daily if he's received any mail. Individuals with autism can have fixated interests.

"To my grandfather (he asks), 'Did I get mail? Did I get mail?' And the answer is no," she said. "I decided it'd be nice for him to get some mail."

And it didn't take long for her campaign to take off.

Postal workers in the small East Coast community said they began noticing an influx of mail addressed to one mailbox.

"There was so much," said Canada Post worker Ian Dewar. "We heard (about it) through some of the people that follow Facebook and it just seemed to catch on."

Heidi Hayes says she is proud of her daughter.

"She's only 15 months older than Kristian," Hayes said. "She is so mature for her age and she carries herself so very, very well and she just loves her brother so very, very much."

With a report from CTV Atlantic's Dan MacIntosh