Phetchaburi's Kaeng Krajan National Park closed the Pa La-oo Waterfall until tomorrow "for tourists' safety" and Chumphon's Pathiu district saw 20 roads and several bridges inundated.

The tropical depression was unusual in that it gathered strength in the Gulf before crossing the peninsula on Tuesday. It unleashed heavy rain from Bang Saphan to Hua Hin. Many villages were flooded and gusty winds damaged 10 houses late on Tuesday night. The front is now over the Andaman Sea.

Dr Anon Sanitwong na Ayutthaya, director of the Southeast Asian bureau of System for Analysis, Research and Training (START), said that the depression was believed to be caused by climate change, as most depressions from the South China Sea hit Thailand in September to October. "This depression in the Gulf was abnormal, it came at an unusual time," he said.

Ban Krud Tambon officials had local residents evacuated to higher ground after two days of heavy rain, amid fears of flash floods from the Tanaosri mountain range.

Hua Hin weather station chief, Sutheep Kaewsornchai, said heavy downfalls had covered 80 per cent of the district for three days and would continue for another day or so. Total rainfall so far was measured as 242 millilitres.

The strong currents caused a bridge on the Hua Hin-Nong Plub Road to subside and become impassable. And a two-kilometre stretch of Petchkasem Highway's Bangkok-bound lane, from Soi Hua Hin 102 to Hua Hin Wittayalai School, was covered with 50-centimetres of water.

Chumphon disaster prevention chief, Veroj Saithongtae, said heavy downpours since Tuesday night had badly affected Tha Sae and Pathiu districts, damaging 20 roads. Several bridges were impassable.

But Chumphon irrigation chief Suraphan Mansornphlaeng was confident floodwaters would not reach Chumphon city, thanks to His Majesty the King's Nong Yai "Monkey-Cheeks" project and the Hua Wang-Panungtuk Canal.

The weather department yesterday warned residents in 10 provinces on the Andaman coast, from Satun up to Kanchanaburi, to brace for heavy rain and flash floods.

The depression was expected to move to north and western areas of Thailand today and tomorrow, and bring more heavy rain.

Mineral Resources Department head Apichai Chawacharoenphan warned people living near mountains and landslide-prone areas to be alert for possible disasters.

In Phang Nga, an emergency rescue centre was set up and heavy machinery was in place near the landslide-prone Khao Sok in Takua Pa and Kapong districts, while the stormy weather prompted officials to urge boats and island-hopping tourists to stay ashore for a few days.

Meteorological Department chief Supareuk Tansriratanawong said statistics from 1951 to 2006 showed that only one major depression had hit Thailand in April - that was back in 1961 - and only six tropical depressions had hit during May.

Most depressions formed in the South China Sea before passing over Thailand. He also said the latest low pressure gathered power in the Gulf, which was unusual.