BANGKOK, Oct. 12 (Xinhua) -- Thai Prime Minister Prayut-chan-o-cha on Wednesday canceled scheduled visits in eastern Thailand and flew back to Bangkok by helicopter, reportedly heading to the hospital where Thai King Bhumibol is being treated.

Prayut did not state the reason for his return to Bangkok in the wake of the cancellation of scheduled visits in two eastern Thailand provinces.

Media reports say the prime minister later changed to a motorized convoy at an army base and headed to Siriraj Hospital.

Messages spread in social media, saying that royal family members are rushing back to Bangkok, with main roads to be closed.

The Thai stock index plunged by 6.8 percent Wednesday afternoon.

The government has called for officials and the public to wear pink, which is the lucky color the King, to pray for him.

There are outpouring of best wishes for the 88-year-old monarch. Thais nationwide are wearing pink to express their best wishes for His Majesty the King's good health as huge crowds of well-wishers flocked to the Grand Palace to sign get-well books for the world's longest serving monarch.

In central province Sukhothai, more than 200 people wearing pink T-shirts joined in chanting prayers for His Majesty the King.

Stating that King Bhumibol's condition was not yet stable at the time it was published, the Sunday statement was different from the confident assurances of previous updates on the monarch's health, who has been beset by illness for years.

According to the 37th announcement by the Royal Household Bureau, royal doctors have performed homodialysis on His Majesty the King and used drugs to control his blood pressure.