British travellers have been warned to avoid all but essential travel to Bangkok due to the threat of “significant” flooding.

The Foreign & Commonwealth Office upgraded its travel advice “against all but essential travel” to the Thai capital and 26 provinces in the country affected by flooding. Heavy rainfall across the country has caused flash flooding and mudslides, causing major disruption and 350 deaths.

The FCO said it changed its travel advice because of the large volume of flood water from the north that needs to pass through Bangkok to the Gulf of Thailand. “High tides will slow the run-off through Bangkok, especially along the Choa Phraya river,” the FCO said.

“As a result, significant flooding is expected in many part of the capital during the October 27-31 period. The flooding is likely to disrupt transport, close tourist attractions and may affect electricity and water supplies, though the authorities have said they will do all they can to maintain these.”

Travellers were warned that cash machines many not work in flooded locations. Hotels “are likely” to have contingency measures in place and travellers should seek advice from hotel management.

Bangkok’s Suvarnabhumi airport currently remains open and can be reached from the city centre. Tourist destinations such as Chiang Mai, Pattaya, Phuket and Koh Samui are not affected and flights are operating to and from them.

Foreign Office minister Jeremy Browne said: “Our thoughts continue to be with the people of Thailand at this difficult time and in the face of unprecedented flooding. However, as prime minister Yingluck Shinawatra has now said that waters will reach the capital, we have updated our travel advice to reflect the worsening situation.”