The number of people experiencing breathing problems increased by 34 per cent on Thursday, London Ambulance Service has said.
The capital experienced "very high" pollution levels yesterday but air quality is expected to improve today.
We saw a 34% increase in patients with breathing problems yesterday compared to an average Thu
People with asthma may also find that they need to use their inhaler more frequently, have it with you at all times
Air quality in London is expected to improve today after the highest level of pollution was recorded on Thursday.
The capital has been blighted by increased levels this week with London Ambulance Service reporting a 14 per cent increase in emergency calls for people experiencing breathing problems.
Tom Cobler, a forecaster for MeteoGroup, said: "The air quality will improve throughout the day. It will edge out to the east over the North Sea as some slightly fresher air mass comes in across the UK from the west."
Meanwhile, David Cameron has been accused of failing to understand the long-term air pollution problem by the European Commission's environment spokesman.
Defra have issued health advice for at-risk individuals as 'very high' pollution levels hit London.
London Ambulance Service revealed earlier that there had been a 14 per cent rise in the number of people calling 999 for help with breathing difficulties.
Masks were seen on the streets of London as air pollution reached "very high" levels in the capital this morning
Boris Johnson must take action and show real leadership on London's pollution problems, Labour have said, as they attacked the mayor's comments that air quality in the capital "seemed perfectly fine".
Onkar Sahota, health spokesman for the London Assembly Labour group, said:
The mayor's comments are dangerously complacent - the London Ambulance Service has seen a 14% increase in people calling them with breathing problems.
In 2008, Boris promised to make London the greenest city in the world. Instead, we've seen wasted opportunities and wasted money.
This latest smog episode should act as a wake-up call to our mayor, whilst sand blown in from the Sahara is a contributing factor, Boris has not taken decisive action to tackle local air pollution.
Boris needs to take action and show real leadership on this issue.
Boris Johnson has dismissed talk of a pollution crisis claiming the air quality seemed "perfectly fine" when he cycled this morning.
"I'm urging people just to have a little balance here, I cycled this morning and it seemed perfectly fine to me," Mr Johnson told ITV London's Simon Harris.
"I think we need to keep a little bit of a sense of proportion. I cycled perfectly happily around today. I understand asthmatics and people who are particularly vulnerable perhaps need to be cautious but there's no reason why people shouldn't go about their daily lives."
The mayor also claimed a Paris-style car ban was not needed to improve London's air quality, adding: "Frankly the position we've got in London is nothing like as bad as that and it's nothing like as bad as it was in Paris a few weeks ago."
London Ambulance Service has seen a rise in the number of people calling 999 for help with breathing difficulties as the capital continues to face "very high" pollution levels.
The service reported a 14 per cent rise in emergency calls for patients with breathing problems yesterday with an average of 200 increasing to 227 calls.
"More people are calling us with breathing difficulties, asthma and heart problems," Deputy medical director Fenella Wrigley said.
Ms Wrigley urged people with asthma to ensure they had their inhalers with them as they may need to use it more frequently in the current conditions.
"This is a busy time for us and I would urge Londoners to use us only in an emergency, and anyone with a minor condition should call NHS 111 or seek advice from their pharmacist or GP," she added.
Pollution in London over the last 24 hours hit 10/10 which are classed as 'very high' levels according to the Met Office and Defra.
To put that in context we have seen nitrogen dioxide levels more than three times higher than the EU legal limit.
David Cameron has revealed that he was forced to cancel his regular morning run due to the "very high" pollution levels.
London and other parts of southern England have been plagued by poor air quality in recent days.
"I didn’t go for my morning run this morning. I chose to do some work instead. You can feel it," the Prime Minister told BBC Breakfast.
“But it’s a naturally occurring weather phenomenon. It sounds extraordinary, Saharan dust, but that is what it is.
Mr Cameron urged people to listen "very carefully" to what the Met Office is saying about the "unpleasant" weather.