National Lottery operator Camelot has apologised after a technical problem left customers across the country unable to buy tickets.
It said the "network communications issue" had affected those buying in-store or via its website on Saturday.
All ticket machines were working as normal after 1800 GMT and the draws went ahead as usual, Camelot added.
A spokeswoman for the Department for Culture, Media and Sport said the glitch was "disappointing".
"Every single pound spent on the Lottery helps good causes across the UK, so it is disappointing to hear that technical difficulties have prevented some tickets being sold," she said.
'Slow transactions'
Camelot said its system went down at about 1400 GMT on Saturday.
A message on the lottery website during the afternoon said: "Our Draw Games are closed. Why not try our exciting Instant Win Games?"
Later, the website began accepting transactions again, but was working slowly due to higher than usual demand.
Camelot's spokesman said the problem had been "intermittent in retailers up and down the country" on Saturday.
It had resulted in either slower than normal transactions or retailers being unable to perform transactions at all, he added.
National Lottery presenter Carole Machin also apologised during Saturday night's live draw show.
Regular player Tracey Birchall, 30, from Bristol, said she was "absolutely gutted".
"I wanted to play my usual numbers but I couldn't. It's so frustrating," she said.
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