A Perth duty free shop attendant has described her devastation at learning a customer was on board missing flight MH370.[Photo/Australia Plus]

A young man who boarded the ill-fated missing Malaysia Airlines flight MH370 had only hours earlier bought a watch in Perth, hoping to surprise his wife back in Beijing, a duty free shop attendant says.

The attendant, who does not want to be named, has told the ABC of her shock at hearing that Xian Wen Shi, 26, was among the 239 people missing and now the subject of a vast land, air and sea search across southeast Asia.

China says one of its satellites has detected three large "floating objects" in a region of the sea where it suspects the missing plane crashed.

The pictures were taken on March 9 at 11:00am local time, the day after the plane went missing, but were only published on a Chinese government website overnight.

Contacting ABC 720 Perth via email, the duty free store attendant says she spent about 40 minutes helping Mr Xian choose gifts from the duty free shop at Perth International Airport.

She says that between Mr Xian's limited English and her limited Mandarin, she learnt that he wanted to buy a present for his wife.

"With my help, he bought a lovely bracelet watch for his wife, and I wished Mr (Xian) and his travelling companion a safe trip back home," she said.

The pair were travelling via Kuala Lumpur, she said, where she learned by checking the passenger manifest that Mr Xian had boarded the Beijing-bound flight that last made contact on Saturday.

The shop assistant says she is still feeling devastated days after a chance meeting with a stranger who did not make it home.

"I just wish to let his wife know that he was thinking about her with the purchase of the watch," she said.

"As for myself and the ones still here, it's a message to make the most of every day, be kind to each other, love your family & friends and be happy with what you have, even in your crappiest day at home or work.

"Remember, you are still here and get to see the sun rise with your love ones."

Malaysia Airlines says it will pass the email on to Mr Xian's wife.

ABC listeners, meantime, have donated money so that the same type of watch can be bought and sent to her.