Police hold grave concerns for a man who has been missing in dense bushland in the Hawkesbury area for more than 24 hours.

A search for Tiemuzhen Chalaer was suspended on Monday night, as temperatures were expected to dip to 4 degrees, and is due to resume at 9am on Tuesday.

The 24-year-old went missing from a campsite party at Lower Portland, near Wheelbarrow Ridge Road track and Greens Road, on Sunday morning.

He was last seen between 6.30am and 9am, when police believe he walked into bushland near the campsite.

Mr Chalaer was reported missing at 8pm on Sunday night, when his friends returned to Sydney and realised the Chinese national wasn’t with them.

Chief Inspector Garry Sims told ABC Radio that a misunderstanding led to the delay.

“It’s one of those situations where everyone else was assuming he was with someone else, and it was only when people returned to their homes in Sydney they realised he hadn’t returned,” Inspector Sims said.

Dozens of police and volunteers launched a search for Mr Chalaer at daylight on Monday.

Local police joined officers from the Public Order and Riot Squad, Police Rescue, the dog squad, State Emergency Service and Rural Fire Service to trek into the bushland to find the 24-year-old.

As well as the ground search, police used a helicopter and a drone to search from the air.

However, no trace of Mr Chalaer was found and the search was suspended at 5pm.

Friends and family took to Facebook to share a photo of the hotel management student, who was described as “the epitome of zen”.

“I hope in God that he is safe. I’m praying for you my friend wherever you are. God be with you,” one friend wrote.

His sister added: “Hello friends in Sydney, please keep an eye out for my brother.”

Police hold grave concerns for Mr Chalaer’s welfare as he has a condition that requires medication twice a day.

It is believed he did not take any supplies with him when he walked into the bushland, which was a chilly 8 degrees on Sunday night.

He was wearing a brown, chequered, button-up shirt, blue jeans, black adidas sneakers, a red scarf and a black leather jacket when he was last seen.

Police remain hopeful Mr Chalaer walked out of the bushland and is safe but hasn’t managed to make contact. Anyone with information on his whereabouts is urged to phone triple zero, or Crime Stoppers on 1800 333 000.