Pakistan floods hit bus, 21 dead

As many as 55 people have been killed across Pakistan since monsoon rains began in July.

As many as 55 people have been killed across Pakistan since monsoon rains began in July. (AAP)

Flash floods triggered by monsoonal rains have swept away a bus carrying a wedding party in northwest Pakistan, killing 21 people.

Local disaster management officials said the incident happened in the Landi Kotal tribal region bordering Afghanistan on Saturday.

At least four people were still missing and it was unclear whether the bride and groom were also travelling in the same bus.

Eight women were among those killed.

Pakistan's National Disaster Management Authority said in statement on Saturday that as many as 55 people have been killed across Pakistan since the monsoon rains started in July.

Flash floods commonly occur during South Asia's summer monsoon season, which ends in September.