Crown Prince Maha Vajiralongkorn returned to Thailand Wednesday amid growing concerns about the health of his father, King Bhumibol Adulyadej.

The Crown Prince was seen making his way to the Siriraj Hospital, where King Bhumibol is being cared for by doctors. It's not yet known if the Crown Prince has visited the King, who remains in unstable condition, according to a Thai palace statement released Wednesday.

As the Thai nation holds an anxious vigil for their beloved King, hundreds gathered in temples and outside Siriraj Hospital. They held framed portraits of King Bhumibol and prayed for his speedy recovery. Well-wishers were dressed predominantly in pink -- an auspicious color believed to restore health -- and yellow, which is the color of the King.

"I have been coming here for 10 years since the King has been ill," Donnapha Kladbupha, a Bangkok resident and private English tutor, told CNN.

"A long time ago, the King told us he would live to 120 years [of age], but it is very difficult for him now. We still hope. He is like an angel to us and I believe he can pass this difficult time," added Kladbupha.

King Bhumibol, 88, ascended to the throne 70 years ago, making him the world's longest-reigning monarch. He is being closely monitored after undergoing medical procedures over the weekend.

With fears around the Thai King's health mounting, a government spokesman urged the Thai public to "rely on official announcements" for any updates. He added that the Thai public should not rely on "uncorroborated information in social media circles."

Messages of support have been flooding social media sites, with well-wishers tweeting under the trending hashtag #LongLivetheKing.

The Crown Prince is expected to meet with Thai Prime Minister Prayut Chan-o-cha, but a government spokesman said in a statement the two would be discussing general affairs.

Thai businessman Sira Singsat, 24, joined the vigil held for the King outside Siriraj Hospital with his mother and sister. He praised the King, calling him a "role model" for the Thai people and a "spiritual leader."

"I have come here to pray. We believe that this will help him to recover," he told CNN. "I guess we are a little bit worried about what happens next, but it is important now to support and pray for our King."

(CNN)