Transport for London (TfL) has advised people using its services over the bank holiday weekend to carry water with them when they travel as temperatures climb above 30C (86F).
London is forecast to see its hottest May day on record on Monday, with temperatures predicted to hit 34C.
A TfL spokesperson said: "Please look out for each other while travelling."
The UK Health Security Agency (UKHSA) issued its first amber heat-health alert of 2026, warning Londoners that high temperatures over the coming days may put vulnerable people at increased risk.
TfL said air conditioned Tube trains covered 40% of the network and all London Overground and the Elizabeth line trains were air conditioned.
On older parts of the Tube network which have fewer ventilation shafts, TfL has introduced a range of station cooling systems including industrial-sized fans.
In addition, every TfL bus has reflective roofs, insulation and opening windows, while all new double-decker buses have air cooling.
The transport operator said it would monitor track temperatures, enhance its response to air conditioning faults and carry out regular checks on moving parts of tracks and crossings to keep the network moving during the heatwave.
Temperatures in London are expected to fall to 24C on Wednesday.
The UKHSA recommends "simple steps" to keep safe during periods of hot weather, including:
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