"We're very sorry that the site is still experiencing problems. We are working urgently to get it back up and running as soon as possible", the committee said on Twitter.
The website crashed at least twice in the last several hours and is now working again, with more than 681,000 signatures at the time of writing. More are being added each second. The parliament is required to consider for debate all petitions that collect more than 100,000 signatures.
Hours later, a petition to revoke Article 50 collected over 1 million signatures. The UK government has to respond to all petitions that gather more than 10,000 signatures. The parliament has to consider for debate the ones that collect more than 100,000 signatures.
The petition calling for Brexit reversal crashed the UK Parliament's website earlier in the day and has racked up about 500,000 additional votes in several hours since it went back up online this morning.
Prime Minister Theresa May is currently in Brussels to negotiate a potential Brexit extension at the European Council.
Tusk said late on Wednesday that a short extension would be possible, but only if the UK House of Commons, which has already rejected the withdrawal deal twice, was able to pass it now.