Embassies in Thailand have advised tourists to respect the feelings of the Thai people following the death of King Bhumibol Adulyadej, a man seen as a father-figure in the country.

King Bhumibol, who was the world's longest-reigning monarch, died on Thursday aged 88, sparking an outpouring of grief.

The government has declared one year of official mourning and asked Thais to wear black and avoid "festivities" for 30 days.

Prime Minister Prayuth Chan-ocha, however, has called on businesses to stay active. The cabinet declared a government holiday for mourning on Friday but the Stock Exchange of Thailand and banks operated normally.

Britain's Foreign Office said in a travel advisory those travelling to Thailand to be respectful of people's feelings.

"You should respect the sensitivities of the Thai people at this time; access to entertainment, including restaurants, bars and shopping areas may be restricted and you should behave respectfully when in public areas," it said.

Tropical Thailand, with its beaches, Buddhist temples and infamous night life, remains a magnate for travellers despite weathering more than a decade of unrest, including two coups, floods in 2011 and a wave of bombs in tourist towns in August.

The country expects a record 33 million visitors this year.

The government has not announced specific restrictions on nightlife but it is at least likely to be subdued.

Thailand's laws protecting the royal family from insult are among the strictest in the world.

Article 112 of the criminal code says anyone who "defames, insults or threatens the king, queen, heir-apparent or regent" will be punished with up to 15 years in prison.

Foreigners have been jailed for breaking the law.

In 2009, an Australian writer was sentenced to three years in prison for a passage in his 2005 novel deemed insulting to the monarchy. He was later released.

In 2007, a Swiss man was sentenced to 10 years in prison for spray-painting graffiti over posters of King Bhumibol, apparently while drunk. He was later released.

"We recommend the following for residents and tourists: exercise caution and observe public order laws ... maximum respect for the sentiment of the Thai people," the Italian Embassy in Bangkok said.

The government said it had increased security around the country following the king's death.

"Stupid behaviour right now is totally out of the question," said Didier Arnault, a French national living in Bangkok's historic quarter near royal palaces.