The city's record was 35.1C, according to experts at the Radcliffe Meteorological Station, which has data stretching back to 1815.

But now some services are reporting that temperatures in the city reached 37C on Thursday. 

Trains services have been disrupted and some businesses closed, with some workers expecting to be sent home. 

ALSO READ: Great Western Railway and Chiltern warn of heatwave delays

The station will not be able to confirm if the record has been beaten until tomorrow, but the Met Office was expecting temperatures in Oxford to reach at least 35C, as the rest of the country bakes. 

Last month also saw one of the city's hottest June days ever recorded. 

ALSO READ: Oxford heatwave - 4th hottest June day ever recorded - 33C

The joint hottest days in Oxford's history were August 19, 1932, and August 3, 1990, when the mercury tipped over 35C, according to a new book called Oxford Weather and Climate since 1767. 

Today's forecasted similar temperature will also impact the records for the hottest July days, which are currently as follows:

• 1              34.8C, July 19, 2006 (also the second hottest day in city history)
• 2              33.9C, July 19, 1825 and July 12, 1923
• 3              33.7C, July, 13, 1923
• 4              33.5C, July 1, 2015
• 5              33.4C, July 3, 1976

The warmest night was July 20, 2016, at 21.2C. 

In its regional forecast, the Met Office explains: "An exceptionally hot and humid day across the region, with plenty of sunshine initially. However, some thundery showers will develop during the afternoon, these perhaps becoming confined to eastern parts later in the evening.

IN PICTURES: Thunder and lightning from earlier this week

"Maximum temperature 39C".

Temperatures in Oxford - 4C lower than in other parts of the area - are expected to peak between 3pm and 5pm. 

ALSO READ: Can I go home from work if it's too hot?

Thunderstorms could happen between 1pm and 2pm, before more muggy weather over the next few days. However, there is potential for some rain tomorrow, the Met Office suggests. 

The Radcliffe station's Ian Curtis, who also works at Oxford University's Environmental Change Institute, said: "The crucial bit is that as well as the extreme hot days, we’re also seeing seasonal shifts. Both are game changers for Oxford people. The upcoming Citizens’ Assembly on climate change must recognise the impact of changes to our local weather –as well as the unique contribution Oxford can make to solving global climate change.

ALSO READ: Oxford 'top trumps' show positivity on climate crisis - opinion

“The new book Oxford Weather and Climate since 1767 has some extraordinary insights into the history of our local weather and how it is changing. No other city in the UK has such a detailed analysis.”

The public are being advised to stay hydrated, wear suncream and keep cool. 

ALSO READ: Warm weather Oxfordshire - Water advice issued

Meanwhile, pet owners have been advised to keep their animals cool and not leave them in cars unattended, particularly while travelling. 

Emma Batchelor, Director of Discover Ferries, said: Planning the right time to travel and ensuring your pets also have their holiday essentials can make the journey even more comfortable for everyone."