Prime Minister Prayut Chan-o-cha casts his ballot in Bangkok on March 24, 2019. (Photo: Xinhua/ VNA)

On Sunday night, the EC delayed without explanation a full announcement of preliminary results as a torrent of complaints mounted over apparent mistakes in the count and possible irregularities at the polls.

Nearly 1.9 million votes have been invalidated with 93% of votes tallied, the EC said late Sunday. Earlier counts showed that in a handful of provinces more than half the ballots cast were invalidated.

The EC said the preliminary vote turn-out will be announced on Friday.