"The most powerful TV station in the world"
 

According to this report ( in Portuguese ) in this 1961 issue of the magazine "Radiolandia" , the station TV Jornal do Comércio of the city of Recife, Northeast of Brazil, had the most powerful transmitters in the world. It was capable of reaching 700 kilometers, it was said that it reached Argentina and could easily be watched in Rio de Janeiro if the viewer had an appropriate antenna.

The report says that nothing like this existed in other parts of the world because in Europe the distances were much smaller and in the USA the stations were linked by coaxial cable and microwave ( by 1961 only three states of Brazil were linked, the rest of the Nation still had only local programming and films ).

Never knew that a TV transmitter this powerful could be built!

How much power did they run? In the US, UHF stations were allowed to run as high as 5 Megawatts (ERP), if you could afford the electric bill.
Most likely the DX reports were a result of E skip:
https://en.wikipedia.org/wiki/Sporadic_E_propagation
And from Portugal to Argentina, most of that would be over water!

How far is 700 kilometers in miles?

This was a VHF station. I don't read the language, but I think it says 50 kW. Of course, it doesn't say if that was ERP, but it probably was.
In the U.S., 5 MW ERP limit was only for UHF. The U.S. ERP limit for low VHF analog was 100 kw.

700 km = 435 miles.

The station was in Brazil, which speaks Portuguese.

Note: IIRC, by the 1990s, when the U.S. was trying to promote its digital TV technology in Brazil, Brazil had a very large number of low power stations, because local politicians wanted to own a station covering their area. On the other hand, the Brazilian TV network Globo dominated the whole country for nationwide programming.

Remember that the ratio between transmitter power and ERP is not fixed. It depends heavily on the antenna. It's easier to get more antenna gain at higher frequencies. For example a UHF 40kW transmitter might give 1MW ERP. That's an antenna gain of about 14dB. You would get a lot less antenna gain at VHF, especially on Band I (Low band).

True. That's why that 50 kw number in a non-technical magazine is so iffy. If it's ERP, it seems too small to be "the most powerful in the world," but on the other hand you would expect a non-technical magazine to list ERP (without saying so) just because it's a bigger number.

In the US:

Low band ERP= 100 Kw.
High band ERP= 316 Kw

Crystal Palace the TX for London & large parts of South East England was 200 Kw's ERP on channel 1. (45 Mhz vision & 41.5 Mhz sound) It was the most powerful TX on low band in UK. it closed down in Jan 1985 along with all other VHF TV TX's & the UK became a UHF only country..